Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9×13 inch baking dish. Cook spaghetti according to package directions until al dente. Drain well and set aside.
Step 2: While the spaghetti cooks, heat olive oil in a large skillet or Dutch oven over medium heat. Add chopped onion, celery, and green bell pepper (if using) and sauté for 5-7 minutes until softened.
Step 3: Reduce heat to low. Stir in both cans of condensed soup, softened cream cheese, chicken broth, garlic powder, onion powder, and black pepper. Stir constantly until the cream cheese is fully melted and the sauce is smooth and creamy. If the sauce is too thick, add milk 1/4 cup at a time until desired consistency.
Step 4: Remove the skillet from heat. Gently fold in the cooked shredded chicken and 1 cup of the shredded cheddar cheese until well combined with the creamy sauce.
Step 5: Add the drained spaghetti to the skillet with the chicken and sauce mixture. Toss until the spaghetti is evenly coated with the creamy chicken spaghetti recipe sauce.
Step 6: Pour the entire creamy chicken spaghetti recipe mixture into the prepared 9×13 inch baking dish. Spread evenly.
Step 7: Sprinkle the remaining 1 cup of shredded cheddar cheese over the top of the creamy chicken spaghetti recipe.
Step 8: Bake for 25-30 minutes, or until the creamy chicken spaghetti recipe is bubbly and the cheese on top is melted and lightly golden. Let it rest for 5-10 minutes before serving.
Step 9: Garnish with fresh chopped parsley, if desired, and serve this delicious creamy chicken spaghetti recipe warm.