Heat oven to 400 degrees. Grease pie plate, 10 x 1 1/2 inches. Brown beef and onion; drain. Spread in plate.

Beat milk, eggs, baking mix, salt and pepper 15 seconds in blender on high or 1 minute with hand beater.

Pour into plate. Bake 25 minutes. Top with tomatoes and cheese. Bake until knife inserted in center comes out clean, 5 to 8 minutes.

6 to 8 servings. High Altitude: Increase first bake time to 30 minutes.