In a large bowl toss together romaine and iceberg or leaf lettuce. Arrange greens on four individual salad plates. Top with shrimp, tomatoes, feta cheese, green onions, and olives.
For dressing, in a screw-top jar, combine olive oil or salad oil, vinegar, oregano, garlic powder, and pepper. Cover and shake well to mix. Pour dressing over salads. Top with the anchovy fillets, if desired. Makes 4 servings.