Preheat the oven to 375 degrees F. Grease a 9×13 or 10×5 casserole dish (ours is a 10×5).
Cook spaghetti according to package instructions for al dente. Drain and place in a large mixing bowl. Add the diced cooked chicken, tomatoes, and fresh parsley. Set aside.
8 oz Spaghetti, 2 cups Chicken, 14 oz Diced tomatoes, 1/2 cup Fresh parsley
In a saucepan melt the butter over medium-high heat. Add the onion and saute until tender. Add the garlic and cook for 1 minute.
1/4 cup Unsalted butter, 1 small Onion, 2 cloves Garlic
Whisk in the flour, oregano, basil, thyme, salt, and pepper. Cook for 1 to 2 minutes.
1/4 cup All-purpose flour, 1/2 tsp Dried oregano, 1/2 tsp Dried basil, 1/4 tsp Dried thyme, 1/2 tsp Kosher salt, 1/2 tsp Black pepper
Gradually whisk in the chicken broth, milk, and half and half until smooth. Cook until thick and bubbly. It should be the consistency of cream soup.
1 cup Chicken stock, 1/2 cup Whole milk, 1/2 cup Half and half
Remove from the heat and stir in the Pecorino Romano and 1 cup sharp cheddar cheese until melted. Season with salt and pepper to taste.
1/2 cup Pecorino Romano, 2 cups Sharp cheddar cheese
Pour the cheese sauce over the spaghetti ingredients and mix until combined.
Pour into the prepared baking dish. Sprinkle the remaining sharp cheese evenly over the top.
Bake for 25-30 minutes or until it’s hot and bubbling. Let rest about 10 minutes before serving.