Chop tomatoes into small cubes, finely slice green onions. Toss with fresh basil.
Whisk together olive oil, vinegar and salt and pepper. Pour over salad mixture. Marinate for at least 2 hours.
Cut yellow pepper in half, removing seeds and pulp. Fill each half with salad mixture. Put the rest of the salad mixture into a bowl. Place on a plate with pepper halves on either side. Garnish.