Bring a large pot of salted water to a boil. Add the spaghetti and cook until just al dente. Drain the pasta well and set it aside. Do not overcook because it will continue cooking later in the oven.

Melt the butter in a large skillet over medium heat. Add the onion and bell pepper. Cook for about five minutes until soft. Stir in the garlic and cook for another minute until it smells fresh and delicious.

Add the cream of mushroom soup, cream of chicken soup, chicken broth, and sour cream. Stir until everything becomes smooth and creamy. Mix in smoked paprika, onion powder, garlic powder, salt, and black pepper for extra flavor.

Place the shredded cooked chicken into the creamy sauce. Stir gently until every piece is coated well. Let the mixture cook for about three minutes so the chicken absorbs the rich flavors.

Add the cooked spaghetti into the skillet. Sprinkle in one and a half cups of cheddar cheese and half a cup of mozzarella. Mix slowly until the pasta is fully covered with the creamy cheese sauce.

Lightly grease a 9x13-inch baking dish. Spoon the spaghetti mixture into the dish. Spread it evenly with the back of a spoon so every serving bakes evenly.

Sprinkle the remaining cheddar and mozzarella over the top. The extra cheese creates a golden and bubbly crust that everyone loves after baking.

Bake in a preheated 350°F (175°C) oven for about 30 to 35 minutes. The cheese should be melted and lightly golden. The sauce should bubble around the edges.

Remove the casserole from the oven. Let it rest for about ten minutes before serving. Sprinkle chopped parsley over the top for fresh color and flavor.