Stir together the tomatoes, garlic, onion, cilantro, jalapeño, lime juice, oil, salt, and cumin. Taste and adjust seasonings if needed. Let it rest for half an hour so the flavors can come together, then serve.
Will last 1 day in the refrigerator, though it may get extra juicy. You can drain some of the juice if you like.
If tomatoes are not ripe and in season, 2 cups chopped grape or cherry tomatoes are a good substitute. Red onion is terrific with this, as well .