To make the salad, tear the lettuce into bite-size pieces and place in a large bowl. Add the cucumber, onion, tomatoes, and pepper. Set aside.
To make the dressing, in a small bowl, combine the oil, vinegar, salt, oregano, and pepper. Mix well. Pour over the salad and toss. Divide the salad among 6 salad plates and top each with a portion of crabmeat, olives, and cheese. Serve immediately.