1 tbsp. sliced ripe olives
2 medium tomatoes, chopped
2 cups torn iceberg lettuce
1 cup shredded part-skim mozzarella cheese
1 cup shredded cheddar cheese
2 taco shells, coarsely crushed
1 can (16 ounces) refried beans
1 prebaked 12-inch pizza crust
1 envelope taco seasoning
1/2 cup water
1 small onion, chopped
1-1/4 pounds ground beef