On large platter, place lettuce. Arrange tomatoes, cucumber, peppers, eggs, celery, green onions, potato, mushrooms and cheese, on lettuce. Cover and refrigerate until serving.
Dressing: In small bowl, whisk together oil, lemon juice, garlic, mustard, salt, pepper and sugar; drizzle over salad just before serving.
Tip: Store any leftover dressing in a sealed jar in the refrigerator.