Preheat the oven to 350°F (180°C), and lightly grease a 9x13 inch baking dish.

In a large skillet, melt the butter over medium heat. Add the onion, red bell pepper, poblano pepper, and jalapeno. Cook for about 3-4 minutes until the vegetables are soft. Add the minced garlic and cook for another minute.

Stir in the chili powder, ground cumin, and garlic powder, and cook for 30 seconds.

Sprinkle the flour over the vegetable mixture and stir well to combine, cook for 30 seconds.

Gradually add the chicken stock, stirring continuously to avoid lumps. Cook for a few minutes until the mixture thickens slightly. Then, add the cooked shredded chicken and diced tomatoes. Season with salt and pepper. Cook for another 5 minutes, then remove from heat and stir in the sour cream.

In a 9x13 inch baking dish, spread a thin layer of chicken sauce on the bottom, then top with 6 corn tortillas. Spread half of the chicken mixture over the tortillas, then sprinkle with half of the shredded cheese. Repeat the layers once more, ending with a cheese layer on top.

Bake in the preheated oven for 35-40 minutes or until the cheese is bubbly and slightly browned.

Allow the casserole to cool for a few minutes before serving. Garnish with fresh chopped parsley.