Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with cooking spray or olive oil.

Coat the chicken with olive oil and sprinkle fajita seasoning over it, mixing well to ensure even coverage.

Heat a tablespoon of olive oil in a skillet over medium-high heat and cook the chicken for 5-7 minutes until browned and cooked through.

In the same skillet, sauté diced bell peppers and onions for 5-6 minutes until softened.

Combine cream cheese, sour cream, chicken stock, instant rice, one cup of cheese, cooked chicken, and sautéed vegetables in a large bowl, season with salt and pepper, and mix until well blended.

Pour the mixture into the greased baking dish, spread evenly, and sprinkle with the remaining cheese. Cover tightly with aluminum foil.

Bake in the preheated oven for 20 minutes, then uncover and bake for an additional 10-15 minutes until the cheese is bubbly and golden.

Allow the casserole to rest for 5 minutes before serving.