Thinly slice the baby red onion, then mix it with ground black lime, red wine vinegar, and salt in a bowl. Let it macerate for 20 minutes.

Whisk together olive oil, pomegranate molasses, red wine vinegar, ground black lime, and salt in a small bowl for the dressing.

Wash and dry the tomatoes. Cut larger heirloom tomatoes into thick discs and halve the cherry tomatoes.

Gently fold halved cherry tomatoes, torn basil leaves, and half of the pomegranate seeds with larger tomato slices. Add dressing and toss.

Arrange thick slices of larger tomatoes on a serving dish, spoon small tomato mixture in the center, top with marinated onions and remaining pomegranate seeds.