Preheat your oven to 350°F (175°C).

In a skillet over medium heat, add cubed chicken breast and cook for about 6-8 minutes until browned.

Add sliced onion and bell peppers to the skillet, and sauté for 5-7 minutes until softened.

In a large bowl, mix the sautéed chicken and vegetables with the creamy sauce and fajita seasoning until well combined.

Grease a casserole dish and pour in the mixture, spreading it evenly.

Sprinkle shredded cheddar and mozzarella cheese over the top of the casserole.

Bake for 25-30 minutes until the cheese is bubbly and golden brown.

Let it cool for a few minutes before serving, garnishing with fresh cilantro if desired.