Bring a large pot of salted water to a boil. Cook the spaghetti until just tender. Drain the pasta and keep it aside while preparing the creamy sauce.

Melt butter in a large skillet over medium heat. Add diced onion and bell peppers. Cook until soft, then stir in garlic and cook for another minute.

Add cream of mushroom soup, cream of chicken soup, and chicken broth to the skillet. Stir slowly until the mixture becomes smooth, creamy, and well combined.

Mix paprika, Italian seasoning, salt, black pepper, and cayenne pepper into the sauce. Stir well so every spoonful is full of balanced and rich flavor.

Fold the shredded chicken into the creamy mixture. Stir gently until every piece is coated and warmed through for a tender and delicious texture.

Add the cooked spaghetti along with one cup of shredded cheddar cheese. Toss carefully until the pasta is completely covered with the creamy chicken sauce.

Transfer the mixture into a lightly greased baking dish. Spread everything evenly with a spoon to help the casserole bake perfectly from edge to edge.

Sprinkle the remaining cheddar cheese and mozzarella cheese over the top. This creates a beautiful golden crust with melted cheese in every bite.

Place the baking dish in a preheated 350°F oven. Bake for about 30 minutes until the cheese is bubbly and lightly golden around the edges.

Remove the casserole from the oven and let it rest for five minutes. Sprinkle chopped parsley on top and serve while warm and creamy.