Preheat the oven to 400˚F.

Make the chicken filling: In a large bowl, mix the shredded chicken with the green chiles, 1 taco seasoning packet, and a third of the shredded cheese. Set aside.

Cook the vegetable filling: In a large skillet, add olive oil and onion. Season with the salt and the second taco seasoning packet and cook over medium-high heat until the onions soften, 4 to 5 minutes. Add the corn and cook for 1 to 2 minutes. Add the black beans and fire-roasted tomatoes and cook for a few minutes to combine flavors and break down the tomatoes a bit. Remove the mixture from the heat and stir in a third of the remaining shredded cheese.

Assemble the casserole: Lightly spray a 9x13-inch baking dish with nonstick spray and line the bottom with 8 overlapping tostada shells. (If you don’t have these, you can use 6 corn tortillas, but the crispy tostadas work best.) Top the tostadas with the chicken filling. Top with 6 corn tortillas to cover most of the chicken layer. Spread the black bean and corn mixture on top of the tortillas. Cover with the last 6 corn tortillas. It’s okay to rip them up to get even coverage. Sprinkle with the remaining cheese.

Bake and serve: Bake the casserole, uncovered, for 30 minutes, until it is bubbling and the top is crispy. Cool it for 5 minutes. Slice portions with a knife and use a spatula to serve. Garnish with sour cream and cilantro. Refrigerate leftovers for up to 5 days or wrap tightly and freeze for up to 3 months. Love the recipe? Leave us stars and a review below!