Dice red onion.  Zest and juice lemon.

In a small bowl, sprinkle some of the lemon juice over the chopped onions while you prepare the other ingredients. This will help reduce the intensity of the onion taste.

Drain the tuna and put it into a medium bowl. Drain and rinse the beans.  Mash half the beans; add to the tuna along with the whole beans. Gently stir to combine. Add the onions, chopped parsley, black pepper, lemon zest, remaining lemon juice and olive oil; mix to combine. Add hot sauce and salt, to taste. If the salad seems a little dry, add a bit more olive oil.

Toast bread and spread each of 4 slices with tuna mixture. Top with lettuce leaves and second slice of bread; cut in half. Serve each with cucumber slices and orange wedges.