If using skirt steak or flank steak, cut it into smaller pieces that will fit into your marinade bowl or bag.
Mix the marinade ingredients.
Dip the steak pieces in the marinade and them place them into a bag or bowl.
Add the marinade and onions to the steak in the bag and marinade for 3-4 hours.
Remove the steaks from the marinade and lay on a rack over a sheet pan to allow them to drain a little.
Remove the onions from the marinade with a spider or slotted spoon and place into a bowl.
Grill the steaks over high heat (a wood fire give the best flavor) for 3-4 minutes per side to medium rare, shooting for about 125 degrees F.
While the steaks are grilling and resting, cook the onions in a skillet.
When done, remove the steaks and let rest for 5 minutes.
After resting, slice the steaks thinly against the grain and arrange on a platter.
Spread the onions over the steak slices and drizzle with any accumulated juices from the cutting board, drizzle with some olive oil, sprinkle with some kosher salt, garnish with cilantro or parsley and serve with lime wedges.