The title about says it all. Oil-packed tuna (especially Italian) is awesome here (as it is in all canned tuna recipes).

4 c arugula, washed, dried, coarsely chopped or torn
1 can tuna, drained, oil reserved if using oil-packed tuna
4 tomatoes, cored and cut into quarters
8 radishes, sliced
extra-virgin olive oil, or drained oil from tuna
lemon juice
salt and pepper, to taste
lemon quarters, for garnish, optional

1. Put arugula on individual salad plates or on a large serving platter. Nestle tuna in the middle of the arugula. Arrange tomato quarters around the edge, and then sprinkle radish slices over all. Drizzle with olive oil an lemon juice, to taste. Season with salt and pepper (less salt if tuna is salted). Serve with lemon slices to squeeze additional lemon juice over salad, if desired.