Making Irresistible Spicy Southern Chicken Spaghetti Casserole is straightforward. Follow these easy steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Cook Spaghetti: In a large pot, cook the spaghetti according to package instructions. Drain and set aside.
3. Sauté Vegetables: In a skillet, heat olive oil over medium heat. Add diced onions and bell peppers. Sauté until softened, around 5-7 minutes.
4. Mix Ingredients: In a large mixing bowl, combine cooked spaghetti, shredded chicken, sautéed vegetables, diced tomatoes with green chilies, cream of chicken soup, milk, Cajun seasoning, garlic powder, salt, black pepper, and red pepper flakes. Stir until all ingredients are well combined.
5. Transfer to Casserole Dish: Pour the mixture into a greased 9×13-inch casserole dish. Spread it evenly.
6. Top with Cheese: Sprinkle shredded cheddar cheese evenly over the top of the casserole.
7. Bake: Place the casserole in the preheated oven and bake for 30-35 minutes, or until heated through and the cheese is bubbly.
8. Garnish: Remove from the oven and let cool for a few minutes. Garnish with fresh parsley if desired.
9. Serve: Scoop out servings and enjoy the comforting, spicy goodness!

This step-by-step guide will help you create a dish that satisfies and impresses.