PREHEAT oven to 400ºF. Mix barbecue sauce and pepper in small bowl; set aside. Brown meat with onions and garlic in large skillet on medium-high heat 8 to 10 min., stirring occasionally. Drain. Add corn and barbecue sauce mixture; mix well.
RESERVE 5 zucchini slices; set aside. Arrange half of the remaining zucchini in single layer on bottom and side of 2-qt. casserole dish. Layer with half of the meat mixture, 1 cup of the cheese, remaining zucchini and remaining meat mixture. Top with reserved 5 zucchini slices and remaining cheese. Cover with foil.
BAKE 20 min. Remove foil. Bake an additional 5 min. until casserole is heated through and cheese is melted.