Begin by boiling a large pot of water. Once the water is boiling, add the spaghetti and cook according to the package instructions until al dente. Once cooked, drain the spaghetti and set aside.
In a large skillet, heat the olive oil over medium heat. Add the shredded cooked chicken and sauté for about 3-4 minutes until heated through.
In the skillet with the chicken, add the cream of mushroom soup, milk, diced tomatoes, garlic powder, onion powder, salt, and black pepper. Stir well to combine and cook for an additional 5 minutes.
Add the cooked spaghetti to the skillet and mix until the pasta is evenly coated with the cheesy sauce. Stir in 1 1/2 cups of shredded cheddar cheese, reserving 1/2 cup for topping.
Preheat your oven to 350°F (175°C). Transfer the cheesy chicken spaghetti mixture to a baking dish, spreading it out evenly. Top with the reserved cheddar cheese.
Bake in the preheated oven for about 15 minutes, until the cheese is melted and bubbly.
Remove from the oven and let it cool for a few minutes. If desired, garnish with chopped fresh parsley before serving.