To make marinade, place oil in a small frying pan over medium high heat. Add onion and sauté until translucent, about 3 minutes. Add garlic. Cook for one more minute. Empty into blender with all other marinade ingredients except beer. Puree. Stir in beer.
Place skirt steak in shallow container. Pour marinade on top and marinate 12-24 hours. Remove steak, pat dry, season with salt and pepper on both sides. Discard marinade.
Preheat grill or griddle to high. Sear steak until dark brown, about 2 minutes on each side. Reduce heat or move from hottest part of grill and cook to preferred temperature. Transfer to cutting board and let rest for 2 minutes. Slice against the grain into 1/2-inch pieces.
Heat oil in large frying pan over high heat. Add onions and sauté until translucent, about 5 minutes. Add garlic, salt, pepper and TABASCO® Chipotle Sauce; cook 1 more minute.
Makes 6-8 servings.