To prepare the tomatoes, quarter them and use your fingers to scape out the seeds into a bowl and set aside. Cut the tomatoes into a small dice (1/4" cubes), and add them to a non-reactive bowl along with the red onion, jicama, chile, sea beans and shiso. Refrigerate ready to serve.
To serve just whisk the lime juice, olive oil, salt and pepper together and pour over the vegetables. Toss gently to coat then plate individual servings, topping with a generous helping of sea urchin and the reserved tomato seeds.