Combine tuna, onion, parsley and olive in medium bowl.
Whisk together olive oil, peel, lemon juice, salt and pepper in a small bowl. Pour about 2/3 dressing over the tuna mixture; toss to evenly coat. Pour remaining dressing over the greens, in another bowl; toss to evenly coat.
Divide tuna mixture among wraps. Top with 1-1/2 cups greens and tomato slices. Roll up wraps.