Preheat the oven to 400°F and position an oven rack in the upper third of the oven. Line a baking sheet with parchment paper or aluminum foil.

Place the tomato halves, onion, jalapenos, and garlic on the baking sheet and drizzle with the olive oil. Using your hands, rub to evenly distribute the oil all over the vegetables. Place the tomato halves skin sides up. Sprinkle with salt and pepper and transfer to the oven. Roast, stirring once or twice, until the jalapeno and tomato skins are charred in places, the vegetables are soft and tender, and the onion quarters are be caramelized around the edges, 20 to 30 minutes. Remove from the oven and set aside until cool enough to handle, then remove the tomato and jalapeno skins and transfer the vegetables to a blender. Remove the peels from the onion and garlic and discard. Add onion and garlic to the blender along with a pinch of salt and pepper and the lime juice. Pulse until a chunky texture is formed. Transfer to a nonreactive bowl and add the cilantro, then season to taste with more lime juice, salt and pepper.

Serve warm or at room temperature with chips, tacos, enchiladas or burritos.

Note:  If a less spicy salsa is desired, you can remove the seeds and membranes from the insides of the jalapenos before processing.