01 - Preheat oven to 350°F (175°C) and generously grease a large casserole dish.
02 - In a large pot over medium heat, sear chicken breasts for 6–7 minutes per side until golden brown and fully cooked. Remove from heat and shred the chicken using forks.
03 - Bring a large pot of salted water to a boil and cook spaghetti for 8–10 minutes until al dente. Drain thoroughly and set aside.
04 - In a large mixing bowl, combine shredded chicken, cooked spaghetti, condensed cream of chicken soup, chopped bell peppers, paprika, cayenne pepper, garlic powder, and half of the shredded cheddar cheese. Mix until thoroughly blended.
05 - Transfer the mixture into the prepared casserole dish. Sprinkle remaining cheddar cheese over the top. Bake for 25–30 minutes until bubbly and golden brown.
06 - Allow the casserole to rest for 5 minutes, then garnish with sliced green onions before serving.