Preheat your oven to 350°F (175°C) and grease a large casserole dish with cooking spray or olive oil.

Cook the boneless, skinless chicken breasts in a large pot over medium heat for 6-7 minutes per side until golden brown and cooked through.

Boil salted water and cook the spaghetti for 8-10 minutes until al dente, then drain and cool slightly.

In a mixing bowl, combine shredded chicken, cooked spaghetti, cream of chicken soup, chopped bell peppers, paprika, cayenne pepper, garlic powder, and half the cheddar cheese. Stir well.

Spread the mixture evenly in the greased casserole dish and top with the remaining cheddar cheese.

Bake in the preheated oven for 25-30 minutes until bubbling and golden brown.

Let the casserole rest for 5 minutes before garnishing with sliced green onions.