01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or nonstick spray.
02 - In a large skillet over medium heat, melt the butter. Add the onion and garlic, sauté until translucent, about 3 minutes.
03 - In a large mixing bowl, combine the cooked onion and garlic, diced chicken, uncooked rice, cream of chicken soup, sour cream, chicken broth, thawed peas and carrots, 1 cup cheddar cheese, mozzarella cheese, salt, pepper, paprika, and thyme. Mix thoroughly.
04 - Transfer the mixture to the prepared baking dish and spread evenly.
05 - Cover the baking dish tightly with foil. Bake for 30 minutes.
06 - Remove foil, sprinkle the remaining 1/2 cup cheddar cheese evenly on top, and bake uncovered for 8 to 10 minutes until cheese is melted and casserole is bubbling.
07 - Let stand for 5 minutes before serving. Garnish with fresh parsley if desired.