1. Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish.
2. In a large bowl, combine cooked chicken, cauliflower, broccoli, and bell peppers.
3. In a separate bowl, mix the sour cream, mayonnaise, garlic powder, onion powder, paprika, salt, and pepper until well combined.
4. Pour the sour cream mixture over the chicken and vegetables. Stir until everything is evenly coated.
5. Transfer the mixture into the prepared baking dish and spread it out evenly.
6. Top with shredded cheddar cheese, ensuring it covers the entire casserole.
7. Bake in the preheated oven for 30-35 minutes, or until the cheese is melted and bubbly and the vegetables are tender.
8. Remove from the oven and let it sit for about 5 minutes before serving.
9. Garnish with fresh parsley if desired.

These straightforward steps will lead you to an incredible casserole that is sure to impress!