Coarsely chop your tomatoes, onion, and jalapeño, removing the seeds and inside membrane of the peppers if you are spice sensitive.
In a large pan, heat one tablespoon of oil over medium heat until it starts to shimmer. Add the tomatoes, onion, jalapeño, garlic, one teaspoon of salt and some black pepper.
Cook the veggies, stirring every now and then, until they get really soft, about 15 to 20 minutes. Add the cilantro and cumin and simmer another 5 minutes, or until the cilantro is wilted and the sauce is fragrant.