Preheat oven to broil and line a rimmed baking sheet with foil. Halve tomatoes and place skin-side down on baking sheet. Sprinkle cut sides with salt. Place jalapeño and onion on baking sheet. Wrap the garlic cloves in a small square of foil and add that to the baking sheet as well.

Place in the oven and roast for about 20 minutes, turning vegetables halfway. If the skins are not yet charred, keep cooking and turning until they are to your liking. If needed, remove garlic packet, onion, and/or jalapeño while the tomato continues to cook.

Once roasted, let cool until easily handled. Remove stem from jalapeño, and cut out seeds if desired. Add tomatoes, jalapeño, onion, and garlic to a food processor and pulse until uniformly chopped. Add cilantro, lime juice, and cumin and pulse until desired texture is reached. Taste and adjust seasoning if needed.

Serve warm or chill in the refrigerator to let flavors meld.