Heat oven to 350°F. Spray 8-inch square (2-quart) baking dish with cooking spray.
Sprinkle broccoli, tuna and 1 1/2 cups of the cheese in baking dish.
In large bowl, stir baking mix, sour cream, milk and eggs with wire whisk or fork until blended. Pour into baking dish.
Bake 30 to 40 minutes or until knife inserted in center comes out clean. Sprinkle with remaining 1/2 cup cheese. Let stand 5 minutes before serving.