For the guacamole, place the onion, garlic, jalapeño, juice of 1 lemon and salt in a bowl and let the salt bleed the juices from onions and chili pepper for 10 minutes. Add the avocados and cilantro and mash. Add more lemon juice, to taste. Mix in the chipotle puree or Tabasco and set aside.
Season the meat with salt and pepper, and combine the marinade: lime juice and zest, beer, oil, garlic, cumin, coriander and pureed chipotle or Tabasco. Coat the beef in marinade and let stand for 1 hour or several hours, refrigerated.
Pre-heat the grill or grill pan to medium-high heat. Grill the flank steak for 12-15 minutes, turning once; flatiron steak 10-12 minutes, turning once; shirt steak pieces for 7-8 minutes, turning once. Rest the steak, then thinly slice against the grain. Char the tortillas on each side in a hot, dry skillet, over a flame or on a grill or griddle for about 30 seconds per side.
Serve the tacos with guacamole and other fixings of choice.