Begin by bringing a large pot of salted water to a boil. Once boiling, add the 10 ounces of dry spaghetti noodles and cook according to the package instructions until al dente. Drain the spaghetti in a colander and set aside.
In a large skillet, melt 2 tablespoons of unsalted butter over medium heat. Add 1 clove of minced garlic and the chopped green bell pepper. Sauté for about 3-4 minutes until the bell pepper is tender and the garlic is fragrant.
Sprinkle 1 cup of all-purpose flour over the sautéed vegetables, stirring continuously for about 1 minute to cook off the raw flour taste. Gradually whisk in 1 cup of heavy whipping cream, followed by 1 cup of chicken broth and 1 cup of milk. Continue whisking until the mixture is smooth and begins to thicken.
Stir in 1 teaspoon of Italian seasoning, salt, and pepper to taste. Allow the sauce to simmer for a few minutes, stirring occasionally to prevent sticking.
Add the 2 cups of shredded cooked chicken and drained 14 ounces of diced tomatoes to the sauce. Stir well to combine everything. Let it simmer for another 5 minutes to heat through and allow the flavors to meld.
Finally, add the cooked spaghetti noodles to the skillet, tossing gently to coat the pasta evenly with the creamy sauce. Sprinkle in 1 cup of shredded mozzarella cheese and stir until melted and incorporated.
