Begin by cooking the spaghetti according to package instructions in a large pot of salted boiling water. Drain and set aside.
In a large skillet, heat the olive oil over medium heat. Add the chopped onion and bell pepper, cooking until softened (about 5-7 minutes). Stir in the minced garlic and cook for an additional minute.
In a mixing bowl, combine the cooked chicken, cream of mushroom soup, cream of chicken soup, chicken broth, 1 cup of cheddar cheese, paprika, salt, black pepper, and milk. Mix until well combined.
Add the cooked spaghetti to the skillet with the vegetables, then pour the chicken mixture over the pasta. Stir gently to combine everything evenly.
Transfer the mixture to a greased 9x13-inch baking dish. Top with the remaining 1 cup of shredded cheddar cheese.
Bake in a preheated oven at 350°F (175°C) for 25-30 minutes, or until heated through and the cheese is bubbly and golden.
Remove from the oven and let it cool for a few minutes before serving. Garnish with chopped fresh parsley if desired.