I adore this combination. I use to eat at this Greek restaurant that would serve a greek salad with a scoop of tuna salad on top.
For the tuna I use a tuna in olive oil drained, grated lemon zest, a little lemon juice, diced red onion, celery leaves from the heart, dill, a little dijon and some mayo.
The salad is arugula, its what I had, feta, kalamata olives, cherry tomatoes, and sliced pepperoncini. I use a bottled lemon vinaigrette , Panera brand.