Heat oven to 400°F. Lightly grease 13x9-inch (3-quart) baking dish. Spread taco sauce evenly over bottom of greased dish.
Separate dough into 10 biscuits; cut each biscuit into 4 pieces. Place biscuit pieces in taco sauce; turn to coat. Sprinkle biscuits with 1/2 to 1 cup of the Cheddar cheese, 1/2 to 1 cup of the mozzarella cheese and the olives; mix gently. Bake at 400°F. for 15 to 18 minutes or until bubbly.
Meanwhile, in large skillet, combine ground beef, bell peppers and mushrooms. Cook until beef is thoroughly cooked; drain.
Sprinkle remaining 1/2 cup Cheddar cheese and 1/2 cup mozzarella cheese over mixture in casserole; top with ground beef mixture. Bake an additional 5 to 7 minutes or until mixture bubbles vigorously around edges.