Preheat your oven to 350°F (175°C).
Cook the spaghetti noodles according to the package instructions until al dente. Drain and set aside.
In a skillet, sauté the diced onions, bell peppers, and minced garlic until they are tender and fragrant.
In a large mixing bowl, combine the cooked spaghetti noodles, shredded chicken, sautéed vegetables, condensed cream of chicken soup, condensed cream of mushroom soup, chicken broth, Italian seasoning, salt, and pepper. Mix until everything is well combined.
Transfer the mixture to a greased baking dish and spread it out evenly.
Sprinkle the shredded cheddar and mozzarella cheese over the top of the spaghetti mixture.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and continue baking for an additional 10 minutes, or until the cheese is bubbly and golden brown.
Once done, remove the chicken spaghetti from the oven and let it cool for a few minutes.
Garnish with fresh parsley before serving. Enjoy your delicious chicken spaghetti!