Adjust oven rack 5 inches from broiler element and heat broiler.
Toss tomatillos, onion, jalapeño, and garlic with oil and place on aluminum foil-lined rimmed baking sheet.
Broil, shaking pan occasionally, until vegetables are lightly charred, 10 to 12 minutes.
Cool slightly, about 5 minutes.
Add vegetables, cilantro, lime juice, and ¼ teaspoon salt to food processor and pulse until coarsely ground, 5 to 7 pulses.
Season with salt to taste.
Serve. (Salsa can be refrigerated for up to 3 days.)
