Cut steak into ½” pieces; transfer to large non-metallic bowl or deep dish. Pour Mojo over steak, making sure all pieces are completely submerged; cover and transfer to refrigerator. Marinate at least 2 hours, or up to 24 hours. Bring steak to room temperature 30 minutes before cooking; drain and discard marinade.
Meanwhile, in small bowl, mix together white onion, cilantro, lime juice and salt until combined; cover and refrigerate until ready to use.
Using paper towel, pat steak dry. Heat oil in large non-stick skillet over medium-high heat. Add steak, making sure not to crowd pan; cook in batches, flipping occasionally, until dark golden brown and cooked through, about 5 minutes per batch; transfer to serving platter; tent with foil to keep warm.
Heat large griddle, cast-iron skillet, or other heavy skillet over medium-high heat. Add enough tortillas to cover surface of griddle; leaving some space between each tortilla. Cook, flipping once, until very lightly charred, warmed through and pliable, about 30 seconds per batch; transfer tortillas to tortilla holder, foil packet, or clean dish towel to keep warm.
To assemble tacos, fill tortilla with meat; garnish with reserved onion-cilantro mixture. Drizzle with taco sauce, if desired. Serve with lime wedges.