Preheat your oven to 350°F (175°C) and grease a large casserole dish.

Cook sliced chicken breasts in a skillet over medium heat for 6–7 minutes per side until fully cooked.

Boil salted water in a pot and cook spaghetti until al dente for about 8–10 minutes.

In a mixing bowl, combine shredded chicken, cooked spaghetti, cream of chicken soup, chopped bell peppers, spices, and half of the cheddar cheese.

Transfer the mixture to the greased casserole dish and top with remaining cheddar cheese.

Bake for 25–30 minutes until the top is golden and bubbly.

Let the casserole rest for 5 minutes and garnish with chopped green onions before serving.