Step 1: Cook Pasta and Prepare Ingredients
Preheat your oven to 375°F (190°C). Grease a 9×13 inch (23x33cm) baking dish. Cook the pasta in well-salted boiling water for 1-2 minutes less than package directions for al dente. Drain and set aside. This ensures it won’t become mushy when baked.

Step 2: Sauté the Vegetables for Flavor Base
In a large skillet, melt 2 tablespoons of butter over medium heat. Add the diced onion and red bell pepper. Sauté for 6-8 minutes until softened. Add the minced garlic and cook for 1 more minute until fragrant. Stir in the undrained green chiles, thawed corn, and black olives (if using). Remove from heat.

Step 3: Build the Rich, Creamy Tex-Mex Sauce
In a large pot or Dutch oven, melt ¼ cup of butter over medium heat. Whisk in the flour and cook, stirring constantly, for 2-3 minutes to make a blonde roux. Gradually whisk in the warm milk and chicken broth until smooth. Cook, whisking frequently, until the mixture thickens and comes to a gentle simmer, about 5-7 minutes. Remove from heat.

Step 4: Complete the Sauce and Combine Filling
Whisk the sour cream and condensed cream of chicken soup into the thickened milk mixture until smooth. Stir in the cumin, chili powder, smoked paprika, garlic powder, onion powder, oregano, and optional cayenne. Season generously with salt and black pepper. Add the sautéed vegetable mixture, the shredded chicken, and the cooked pasta to the sauce. Gently fold everything together until evenly combined. Stir in 2 cups of the shredded cheddar cheese and all of the Monterey Jack cheese until melted and cohesive.

Step 5: Assemble the Casserole
Pour the creamy chicken and pasta mixture into the prepared baking dish, spreading it into an even layer. Sprinkle the remaining 1 cup of shredded cheddar cheese evenly over the top.

Step 6: Create the Signature Buttery Cracker Topping
In a medium bowl, combine the crushed crackers, melted butter, and ½ teaspoon of chili powder. Toss until the crumbs are evenly moistened. Sprinkle this mixture evenly and generously over the cheese layer, covering the entire surface.

Step 7: Bake to Golden, Bubbling Perfection
Place the casserole in the preheated oven. Bake, uncovered, for 25-30 minutes, or until the topping is deep golden brown, the cheese is bubbling around the edges, and the filling is hot throughout. If the topping browns too quickly, tent loosely with foil.

Step 8: Rest, Garnish, and Serve
Remove from the oven and let the casserole stand for 10-15 minutes before serving. This allows the filling to set for clean serving. Garnish liberally with sliced green onions and fresh cilantro just before bringing it to the table.