Step 1: Marinate and Cook the Chicken & Veggies
In a bowl, toss the chicken strips with 1 tablespoon olive oil, the fajita seasoning, and lime juice. Let marinate for 15-30 minutes. Cook pasta in salted boiling water for 2-3 minutes LESS than package directions for al dente. Drain and set aside. Preheat oven to 375°F (190°C). Grease a 9×13 inch baking dish.

Step 2: Sauté the Fajita Vegetables
In a large skillet or Dutch oven, heat the remaining 1 tablespoon olive oil over medium-high heat. Add the sliced bell peppers and onion. Sauté for 8-10 minutes, stirring occasionally, until they are tender-crisp and have some charred spots. Remove to a plate.

Step 3: Sear the Chicken
In the same skillet, add the marinated chicken in a single layer (cook in batches if needed). Sear for 4-5 minutes per side, until golden brown and cooked through. Remove to the plate with the peppers and onions.

Step 4: Create the Creamy Fajita Sauce
In the same skillet (don’t wipe it out—the browned bits are flavor!), melt the butter over medium heat. Whisk in the flour and cook for 1-2 minutes to form a blonde roux. Gradually whisk in the warm milk and chicken broth until smooth. Cook, whisking frequently, until thickened, about 5-7 minutes. Reduce heat to low.

Step 5: Finish the Sauce
Whisk in the cubed cream cheese and sour cream until completely smooth. Stir in the salsa, 1 teaspoon cumin, and ½ teaspoon chili powder. Taste and adjust seasoning. Remove from heat.

Step 6: Combine All Components
To the skillet with the sauce, add the drained al dente pasta, the cooked chicken, and the sautéed peppers and onions (including any accumulated juices). Gently fold everything together until evenly coated. Stir in 2 cups of the Monterey Jack cheese and 1 cup of the cheddar cheese until melted into the mixture.

Step 7: Assemble and Top with Cheese
Pour the mixture into the prepared baking dish, spreading it evenly. Sprinkle the remaining 1 cup of Monterey Jack and 1 cup of cheddar cheese over the top. Follow with the grated Cotija or Parmesan cheese. For extra crunch, sprinkle the crushed tortilla chips evenly over the cheese.

Step 8: Bake to Golden, Bubbling Perfection
Bake, uncovered, for 25-30 minutes, or until the cheese is completely melted, bubbly, and golden in spots, and the casserole is heated through. If the top browns too quickly, tent loosely with foil.

Step 9: Garnish and Serve
Remove from oven and let rest for 10 minutes. This allows the sauce to set for perfect serving. Garnish lavishly with sliced green onions and fresh cilantro. Serve hot with lime wedges on the side for squeezing over each portion