How to Make It
Place tuna cubes in a medium bowl. Place watermelon cubes in a separate medium bowl. Process ponzu sauce, vinegar, sesame oil, mirin, tahini, ginger, and chile-garlic sauce in a blender until smooth, 2 to 3 minutes. Pour half of the ponzu mixture over tuna in bowl; pour remaining mixture over watermelon in separate bowl. Cover bowls; marinate in refrigerator to desired taste, 1 to 2 hours. To serve, assemble tuna and watermelon with desired serving options in serving bowls.