1. For the salsa verde: Heat a griddle, grill, or skillet over high heat and add the tomatillos, garlic, and jalapenos all at once. Eyeball them, but do about a minute or two on each side, turning with tongs, until everything is close to getting black but not black.
2. Put the charred vegetables in the blender with the avocado, water, and salt and blend until smooth. Add the cilantro and blend again.
3. For the steak: Combine the seasonings in a small bowl. Squeeze the limes over the meat evenly, using all their juices. Then rub the lime halves over the meat to get the pulp over it. Sprinkle the seasoning mix over both sides.
4. Heat a grill to medium-high. Grill the steak to your liking; we like it medium-well. Remove, let rest 5 minutes, and then slice it across the grain in angled strips. Using 2 tortillas per taco, pile in some meat, onion, and cilantro and top with salsa verde.
If the steak is really thick, ask the butcher to butterfly it and remove some of the fat-but not all, because it adds flavor. The steak should be medium thick, not too thick or too thin-about 3/4 to 1 inch thick.
From Guy Fieri's More Diners, Drive-Ins and Dives book. Adapted from a recipe courtesy of Tony Anteliz of Cemitas Puebla.