This Southwestern squash casserole is one of those dishes that arrived in my kitchen as a busy weeknight solution and then quietly became a star at every potluck and cookout. I first tested this combination late one summer when yellow squash was overflowing from my farm share and I wanted something that could stand up to smoky grilled meats and spicy beans. The result is a comforting layered bake that is creamy from cheddar yet bright from fresh onions and a little tang from salsa. It is spicy enough to feel Tex Mex but mild enough that the whole family reaches for seconds.

What makes this dish special is the balance of textures and flavors. The squash becomes tender but not mushy, the cheese melts into a golden blanket, and the pockets of green chile and jalapeño deliver zip with every bite. I love how it travels well for potlucks and how simple it is to scale up. When I first brought it to a neighborhood barbecue everyone wanted the recipe and the empty pan returned with a few napkins stuck to the bottom. It is reliable, forgiving, and deliciously bold.

Ingredients

• Yellow squash: 7 medium yellow squash, sliced. Choose firm squash with bright skin and no soft spots. Slicing evenly helps the layers cook at the same rate; a hand held mandoline slicer makes this quick and uniform.
• Shredded cheddar cheese: 2 1/2 cups shredded cheddar cheese, divided. I use a sharp cheddar for depth; use a rotary cheese grater for best shred and melting. You can substitute a Mexican blend for a milder, more melty finish.
• Sweet onion: 1 medium sweet onion, chopped. Vidalia or Walla Walla are mild and sweet and work beautifully to balance the heat from the chiles.
• Green chiles and jalapeños: 1 4 ounce can diced green chiles, undrained and 1 4 ounce can diced jalapeños, drained. Canned is convenient and consistent; drain the jalapeños to control excess liquid.
• All purpose flour: 1 4 cup all purpose flour. This binds juices and creates a light creaminess without adding heavy dairy or roux.
• Seasonings: 1 2 teaspoon ground cumin and 1 2 teaspoon salt. These small additions add warmth and bring out the natural flavors of the squash and onions.
• Salsa: 3 4 cup salsa. Choose your favorite jarred salsa or use a fresh salsa recipe for brighter flavor. My favorites are Mateo s, Kylito s, and Pace.
• Green and red onions: 4 green onions sliced and 1 4 cup chopped red onion for a fresh crunchy garnish.

Instructions

Preheat and prepare pan: Preheat the oven to 400 degrees Fahrenheit. Lightly spray a 9x13 inch baking dish with cooking spray to prevent sticking and aid in browning. Set the prepared pan aside while you combine ingredients. This step ensures your squash does not release excess moisture directly onto a cold pan which can slow the cooking process. Combine vegetables and seasonings: In a large mixing bowl, add the sliced yellow squash, 1 cup of shredded cheddar, chopped sweet onion, undrained diced green chiles, and drained diced jalapeños. Sprinkle the 1 4 cup flour evenly over the mixture, then add 1 2 teaspoon cumin and 1 2 teaspoon salt. Toss gently to combine so the flour coats the vegetables; this helps absorb excess liquid and produces a light binding effect as it bakes. Transfer to pan and bake covered: Transfer the squash mixture to the prepared baking dish and press it into an even layer. Cover the dish with foil and bake in the preheated oven for 30 to 40 minutes. You are looking for the squash to become fork tender and for some steam to have released. If the squash still seems firm at 30 minutes keep it covered and check every 5 minutes. Add salsa and finish baking: Remove the pan from the oven and carefully uncover. Spoon the salsa over the top in an even layer, then sprinkle the remaining 1 1 2 cups shredded cheddar evenly. Return the dish to the oven, uncovered, and bake for an additional 10 to 15 minutes until the cheese is melted and beginning to brown at the edges. Look for bubbling cheese and a golden top as visual cues that it is done. Garnish and rest: Remove from the oven and let rest for 5 minutes to allow the filling to settle. Top with sliced green onions and chopped red onion just before serving for brightness and a fresh crunch. Resting also makes portioning easier and prevents hot cheese from sliding off when scooped.

Storage Tips

To store, cover the cooled casserole tightly with foil or transfer into an airtight container. Refrigerate for up to four days. For longer storage freeze the assembled casserole before the final cheese top. Wrap the pan securely in plastic wrap and then foil, or place individual portions in freezer safe containers. Thaw in the refrigerator overnight before baking. Reheat individual portions in a microwave for 1 to 2 minutes or in an oven at 325 degrees Fahrenheit for 15 to 20 minutes until warmed through. Use glass or metal pans for oven reheating and avoid thermal shock by not moving straight from freezer to hot oven without thawing.

Ingredient Substitutions

If you prefer less heat substitute canned mild green chiles for the jalapeños and choose a mild salsa. For a lighter dairy profile use a reduced fat cheddar or a half amount of cheddar combined with Monterey Jack. To make it gluten free replace the 1 4 cup all purpose flour with 1 4 cup gluten free flour or 3 tablespoons of cornstarch mixed into a small amount of salsa to avoid clumping. For a different flavor profile swap half the squash for zucchini; the texture will be similar and the dish will remain moist and flavorful.

Serving Suggestions

This casserole pairs well with grilled chicken, carne asada, or a black bean and corn salad. Serve alongside warm tortillas and a simple avocado salad for a complete Tex Mex spread. Garnish with fresh cilantro, a squeeze of lime, or a dollop of sour cream to add creaminess and brightness. For a heartier meal serve over cilantro lime rice and top with chopped fresh tomatoes or pickled onions for added acidity.

Cultural Background

The flavors in this preparation pull from Southwestern and Tex Mex traditions where chiles, cumin, and salsa are common accents to vegetables and cheeses. Casseroles became popular in American home cooking as a convenient method to combine ingredients and bake them together for family style serving. This dish adapts those regional staples into an easy vegetable forward bake that showcases seasonal summer squash while honoring bold Southwestern flavor combinations.

Seasonal Adaptations

In summer use the freshest yellow squash or a mix of squash and zucchini for a lighter, fresher result. In cooler months roast the squash first to concentrate flavor before combining with the other ingredients. For a holiday table consider adding a layer of roasted poblano strips or swapping cheddar for a smoked cheddar to add a festive depth. You can also add cooked corn kernels in late summer for a sweet contrast to the chiles.

Meal Prep Tips

Assemble the casserole in the morning, cover, and refrigerate up to 24 hours before baking. This is helpful when you are juggling multiple dishes. If transporting to a potluck bake it at home and reheat at the venue or bake there using a disposable 9x13 inch pan. Bring extra salsa and chopped green onions for a final garnish. Portion into individual containers for lunches and reheat gently to keep the texture of the squash from becoming too soft.

This Southwestern squash casserole is bold, versatile, and reliably loved. It s an easy way to turn abundant summer produce into a dish that feeds a crowd and fits seamlessly into Tex Mex meals. Try it once and it will be the one you bring to every barbecue.