Preheat oven to 400°; spray 8" square baking dish with cooking spray. In large bowl, stir chicken, broccoli, stock, rice, ¼ cup Parmesan cheese, oregano, garlic powder, salt and pepper. Spread chicken mixture in prepared dish; sprinkle with Cheddar cheese and remaining ¼ cup Parmesan cheese.
Cover dish tightly with aluminum foil and bake 45 minutes; remove foil and bake 15 minutes or until rice is tender, internal temperature of chicken reaches 165° and edges are bubbly. Let stand 10 minutes. Makes about 8 cups.