This is a fun recipe because the tomato and watermelon look very similar when diced, and they complement each other extremely well. Plus, it's customizable: you can add as much or as little of each ingredient as you prefer to make this bright summer salad.
Peel tomatoes: Bring a pot of water to a boil. Cut an "X" on the bottom of each tomato, then place into boiling water for about 10 seconds. Remove and discard peel; chop tomatoes and set aside. Remove watermelon rind: Slice off the bottom and top, then stand it upright on its flattened base. Remove the rind by carefully cutting strips away from top to bottom, following the flesh of the watermelon. Once the rind has been removed, slice the watermelon into rounds, then into strips. Chop the strips into a dice the same size as the tomato pieces. There should be equal amounts of tomato and watermelon.
Peel ginger with a vegetable peeler or the back of a knife; grate on a Microplane directly into the tomato-watermelon mixture. Add rice vinegar and olive oil. Sprinkle a reasonable amount of salt to balance the sweetness of the tomatoes and watermelon, making it savory. Add a few cranks of pepper and gently mix. Taste to adjust seasonings, and add more salt and grated ginger if necessary. Then gently toss again. Place in a serving bowl. Using scissors, thinly cut leaves of opal basil directly on top of the tomato-watermelon salad before serving.