Add the lettuce, tomatoes, onions, pepper, olives, and croutons to a large mixing bowl. Gently toss everything together until evenly combined.
6 cups chopped iceberg lettuce, 2 roma tomatoes, 1/2 cup thinly sliced red onion, 1 cup whole pepperoncini peppers, 1/2 cup whole black olives, 1 cup croutons