Preheat the oven to 375°F.
In a large bowl, combine the shredded chicken, drained diced tomatoes, cream of celery soup, cream of chicken soup, chopped onion, minced garlic, dried parsley, dried basil, sour cream, and 1 cup of shredded Monterey Jack cheese. Mix well.
Add the cooked spaghetti to the chicken mixture and toss to coat evenly. Season with salt and pepper to taste.
Transfer the mixture to a greased 9x13-inch baking dish and spread it out evenly.
Sprinkle the remaining Monterey Jack Cheese and parmesan cheese evenly over the top of the casserole.
Bake uncovered for 30-35 minutes or until the casserole is bubbly and the topping is golden brown.
Remove from the oven and let it cool for 10 minutes.
Then the casserole is ready to serve and enjoy!
