Heat broiler to high and position a rack in upper third of oven.
Place tomatoes and jalapenos skin-side up on a large rimmed baking sheet with garlic cloves and onion. Broil until skin on tomatoes and pepper are blistered and charred, about 5 to 7 minutes. Set aside to cool for 5 minutes. Remove as much of the charred skin as possible from the tomatoes and peppers. Remove skin from the garlic.
Place vegetables into a food processor with cilantro, lime juice, cumin and salt. Pulse until desired consistency. Serve warm or chilled.