Place a comal or a cast-iron skillet over medium-high heat; do not oil. Place garlic, onion, and tomato (all with their skins) in pan and roast, turning, as needed, with tongs, until blistered and charred all over. Let vegetables cool slightly, then peel off skins.
In a blender, combine vegetables with chipotle chile and cilantro leaves. Whirl until coarsely pureed. (If using a mortar and pestle, finely chop cilantro leaves with cooked, peeled onion and garlic. Mash tomatoes and chipotle in mortar, then stir in chopped vegetables and cilantro). Squeeze lime juice into salsa, then stir in oil. Taste, season with salt, and serve. Can be made ahead, covered, and refrigerated up to 3 days.