In a small bowl, whisk together the lemon juice, garlic, salt, and oil. Stir in the oregano and pepper to taste. Set aside.
When ready to serve: In a large bowl lightly toss the lettuce with some of the dressing. Divide the lettuce among 4 salad bowls. Scatter the olives, cheese, cucumber, tomatoes, onion, and peppers over the top of the greens. Serve and pass the remaining dressing at the table.