In a bowl, combine red onion, olive oil, salt, and pepper. Let it marinate for about 5-10 minutes.

Slice the ripe tomatoes and arrange them on a serving plate.

Pour the marinated onion and olive oil mixture over the sliced tomatoes. Season with additional salt and pepper if desired. Garnish with sliced fresh basil and olives.

Divide the prepared salad evenly among 4 plates and serve immediately.