Prepare the marinade: whisk together citrus, oil, garlic, and spices.
Marinate the steak: place flank steak in a shallow dish, pour in marinade, and refrigerate at least 15 minutes.
Preheat grill or grill pan to high; remove steak from marinade and grill until medium, about 4 minutes per side.
Let steak rest 5 minutes, then thinly slice against the grain.
Warm tortillas: heat corn tortillas on the grill or in a dry skillet until pliable.
Assemble tacos: top each tortilla with sliced steak, onion, cilantro, and salsa; serve with lime wedges.