Sprinkle tomatoes with Maldon salt, set aside.
In a small colander, rinse and drain the beans, set aside.
Season tuna with salt and pepper, and sear in a hot pan with a little olive oil until just grilled on the outside and cooked about 1/8 inch into the fish. Set aside.
Toss arugula in salt, lemon juice and olive oil, divide onto 2 plates.
Arrange tomatoes, olives, beans on the arugula.
Slice the slightly cooled tuna and fan the pieces on top of the salad. Scatter drained Salsa Criolla (pickled red onions) over the top. Finish with freshly ground pepper and serve.