01 - Preheat your oven to 375°F. Grease a 9x13-inch baking dish thoroughly with butter or nonstick cooking spray.
02 - Melt the butter in a large skillet over medium heat. Add the chopped onion and minced garlic, sautéing until translucent and fragrant, approximately 3 minutes. Remove from heat and set aside.
03 - In a large mixing bowl, combine the sautéed onion and garlic with the cooked chicken, uncooked rice, condensed cream of chicken soup, sour cream, chicken broth, peas and carrots, 1 cup of cheddar cheese, mozzarella cheese, salt, black pepper, paprika, and dried thyme. Mix thoroughly until all ingredients are evenly distributed.
04 - Pour the mixture into the prepared 9x13-inch baking dish. Spread the mixture evenly across the dish using a spatula to ensure uniform cooking.
05 - Cover the baking dish tightly with aluminum foil. Bake in the preheated oven for 30 minutes to allow the rice to cook and absorb the liquid.
06 - Remove the foil from the baking dish. Sprinkle the remaining ½ cup of shredded cheddar cheese evenly over the top of the casserole. Return to the oven and bake uncovered for an additional 8 to 10 minutes, or until the cheese is fully melted and the casserole is bubbling around the edges.
07 - Remove the casserole from the oven and allow it to rest for 5 minutes before serving. This resting period helps the casserole set and makes serving easier. Garnish with fresh chopped parsley if desired.