To assemble the salad, put the lettuce, tomato, cucumber, and your favorite optional vegetable toppings in a large bowl. Add salt and pepper and toss. Just before serving add dressing a little at a time and toss again. Repeat if needed until the salad is as dressed as you like. If you're not sure, err on the side of caution. You can always add more dressing, but you can't take it away. Top the salad (or individual salads) with any toppings that need to stay crunchy--croutons, fried onions, etc.--and serve.