Cebollitas asadas (griddle- or grill-roasted knob onions)

Cut off a chunk of the green tops, leaving about 8 inches.

Coat the onions with oil on both sides and season them.

Lay them on the preheated griddle on their sides with the green parts hanging over, a piece of foil protecting the greens. The same method works on a grill.

Cook slowly, turning, about 15 minutes, until softened and browned in splotches.

Transfer to a plate to serve alongside tacos, or cut up as a taco garnish.

Sprinkle with fresh squeezed lime juice.