Set an oven rack about 6 inches from the heat source and preheat the oven's broiler. Line a baking sheet with aluminum foil.

Combine tomatoes, onions, serrano peppers, and garlic in a large bowl; drizzle with vegetable oil and toss until lightly coated. Transfer to the prepared baking sheet.

Broil in the preheated oven until vegetables begin to brown, about 5 minutes.

Transfer vegetables to the bowl of a food processor. Add salt and cumin; pulse a few times until desired chunkiness is reached. Add cilantro and pulse a couple of times to combine. Stir in lime juice.