Step 1: In a large skillet, melt 2-3 tablespoons of butter over medium heat. Add the finely chopped bell peppers and onion, sautéing until they are tender, about 5 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Step 2: Add the chopped shrimp to the skillet. Cook until they turn pink and are cooked through, about 3-4 minutes. Stir in the cilantro, salt, cumin, and chili powder. Mix well and remove from heat.
Step 3: In a separate saucepan, melt 2 tablespoons of butter over medium heat. Whisk in 2 tablespoons of flour and cook for about 2 minutes until light golden. Gradually add 1 cup of chicken broth, whisking continuously to prevent lumps. Stir in 1 cup of sour cream, 1 teaspoon of garlic powder, and 1 cup of diced canned chilies. Season with salt and pepper to taste. Cook until the sauce is heated through and slightly thickened.
Step 4: Preheat your oven to 350°F (175°C). Spread a thin layer of the green enchilada sauce or salsa verde on the bottom of a 9x13-inch baking dish. Take a tortilla, spoon some of the shrimp filling down the center, and roll it up tightly. Place the enchilada seam-side down in the baking dish. Repeat with the remaining tortillas and filling.
Step 5: Pour the remaining sauce over the assembled enchiladas, ensuring they are well covered. Sprinkle the shredded Monterey Jack cheese evenly over the top.
Step 6: Bake in the preheated oven for about 20-25 minutes, or until the cheese is bubbly and slightly golden.