Preheat oven to 350°F (175°C) and grease a large casserole dish.
Cook the chicken over medium heat for 6-7 minutes per side until golden brown, then shred it.
Boil salted water and cook the spaghetti until al dente (8-10 minutes). Drain and set aside.
In a mixing bowl, combine shredded chicken, cooked spaghetti, cream of chicken soup, chopped bell peppers, paprika, cayenne pepper, garlic powder, and half of the cheddar cheese. Stir well.
Transfer the mixture into the casserole dish and sprinkle the remaining cheddar cheese on top.
Bake for 25-30 minutes until cheese is bubbly and golden brown.
Let sit for 5 minutes, garnish with green onions, and serve.
Notes
Store leftovers in an airtight container for up to 3-4 days in the refrigerator or freeze for up to 3 months.