Place onion in a sieve; rinse with hot water. Drain well. Combine onion and beans in a microwave-safe bowl. Microwave at high 3 minutes or until heated. Stir in 1 1/2 cups cheese.
Stack tortillas; wrap stack in damp paper towels, and microwave at high for 1 minute or until soft. Pour half of sauce in bottom of a 13 x 9-inch baking dish; dip both sides of each tortilla into sauce. Spoon about 1/4 cup bean mixture down center of each tortilla; roll up. Arrange tortillas in baking dish; top with remaining enchilada sauce and 1/2 cup cheese. Bake at 400° for 8 minutes or until thoroughly heated. Top each serving with sour cream, olives, and cilantro.