Preheat the oven to broil.
Arrange the tomatoes, jalapeños, white onions and garlic cloves in a baking dish or well-seasoned cast-iron skillet, drizzle with oil and toss to coat.
Broil the vegetables in the oven for 12 minutes or until charred.
If using a food processor or blender with a plastic pitcher or bowl, allow the vegetables to cool (plastic, heat and food do not mix). Purée with cilantro, lime juice and salt. Taste and add more lime juice or salt if necessary.
Store leftovers in the refrigerator for up to a week.