Preheat your oven to 350°F (175°C). Grease a large casserole dish.
Cook the chicken in a large pot over medium heat for about 6-7 minutes per side until golden and cooked through.
Boil salted water and cook spaghetti until al dente (8-10 minutes). Drain and set aside.
In a bowl, mix shredded chicken, cooked spaghetti, cream of chicken soup, bell peppers, paprika, cayenne pepper, garlic powder, and half of the cheddar cheese until well combined.
Transfer the mixture to the greased casserole dish and top with the remaining cheddar cheese.
Bake for 25-30 minutes until bubbly and golden brown.
Let it rest for 5 minutes before garnishing with sliced green onions and serving.