In a large bowl, add shredded boneless chicken, diced tomatoes, sliced bell peppers, onions, sour cream, and chicken broth, half of the shredded Mexican cheese, panko breadcrumbs, and fajita seasoning. Mix well.
Prepare the casserole dish by greasing it with cooking oil. Pour the mixture into the casserole dish and spread it evenly using the back of the spoon.
Place the casserole dish in a preheated oven for 15 minutes at 325 degrees F.
Two minutes before the timer goes up, take the casserole dish out of the oven, spread the leftover shredded cheese evenly on the top of the casserole. Place it back in the oven and let the cheese melt and get a golden color.
Once done, take the casserole out of the oven, and garnish it with freshly chopped cilantro. Enjoy!