Preheat oven to 350°F. Spray a 9X13 inch baking dish with nonstick cooking spray.
In a large mixing bowl, mix the first 8 ingredients until evenly combined. Add the chicken (2-3 cups), broccoli (3 cups), and rice (3 cups) and fold until evenly coated and ingredients are mixed. Pour into prepared pan.
Sprinkle the top of the casserole evenly with grated cheese (2 cups). In a small bowl, mix together panko (1 1/2 cups), dried thyme (1 teaspoon), and melted butter (1/3 cup). Sprinkle evenly over the cheese layer. Bake in preheated oven 30-35 minutes or until casserole is heated through and panko crumbs are golden brown.
Baking Dish – Use a 9×13 baking dish and spray it with nonstick cooking spray. This will make clean-up a breeze.
Preheating Oven– Ovens preheat differently and some are designed to use both a top and bottom element to preheat quickly. If food is already in the oven, this quick blast of heat can char the outside while leaving the inside raw. So, you definitely want to preheat your oven before baking this to achieve the best results.