What could be more complicated that lettuce? But if you are looking for a little be more nutrition consider what else might go on your burger or rough cut into your next mix of sauteed vegetables for a side dish. Adding something nutritionally rich makes a difference in energy. Bitter and strong greens that are often difficult for some to eat raw, ease their flavor when lightly cooked. Higher nutrient numbers offer more body energy.
Take a look at these greens and their nutritional density index and see if you might want to add them to balance your own meals. The Vegetable Alchemist.