Step 1

Combine chili powder, ground cumin, onion powder, paprika, pepper, and garlic in a small bowl and set aside.

Step 2

Preheat oven to 350 degrees F (175 degrees C) and spray an 11x7-inch baking dish with cooking spray.

Step 3

Place water and bouillon cube in a microwave-safe container and microwave on high for 2 minutes; stir until bouillon cube is dissolved. Cool slightly, add milk, and set aside.

Step 4

Melt butter in a small saucepan over medium heat until bubbly, about 2 minutes. Stir in flour and cook, stirring constantly, about 2 minutes. When flour and butter are bubbly and thickened, gradually stir in milk-bouillon mixture. Cook, stirring, until the mixture boils and thickens, 3 to 5 minutes. Remove from heat and stir in 1 1/2 cups Cheddar cheese.

Step 5

Combine chicken, black beans, corn, tomatoes, and spice mixture in a bowl; mix well. Pour in cheese sauce and stir again. Pour casserole ingredients into the prepared baking dish.

Step 6

Bake in the preheated oven for 25 minutes. Sprinkle crumbled tortilla chips over the casserole, return to the oven, and bake until casserole is bubbly and set, about 10 more minutes.

Step 7

Remove from the oven and allow to cool, about 10 minutes. Sprinkle reserved Cheddar cheese and chopped tomatoes evenly on top of the casserole, then add dollops of sour cream.