To make the mojo - with a mortar and pestle, mash together the garlic, jalapeños, cilantro, salt, and pepper to make a paste.
Put it in a glass jar.
Add the lime and orange juices, the vinegar, and the oil and shake it up to combine.
Lay the flank steak in a large baking dish and pour the mojo over it.
Wrap tightly in plastic wrap and refrigerate for 1 hour or up to 8 hours, so the flavors can sink into the meat. (Don’t marinate the steak for more than 8 hours or the fibers will break down too much and the meat will get mushy.).
Preheat an outdoor grill or a ridged grill pan over a medium-high flame (you can also use your broiler).
Take a few paper towels and fold them several times to make a thick square.
Blot a small amount of oil on the towels, then carefully and quickly wipe the hot grates to make a nonstick grilling surface. Pull the steak out of the mojo marinade and season on both sides with salt and pepper. Grill (or broil) the steak for 7 to 10 minutes per side, turning once, until medium-rare.
Remove to a cutting board and let it rest for 5 minutes to allow the juices to settle.
Slice thin on an angle, across the grain.
While the steak is resting, warm the tortillas for 30 seconds on each side in a dry skillet or on the grill, until toasty and pliable.
To serve, put two of the warm tortillas on your work surface.
Lay about an eighth of the beef down the center of each, and sprinkle with lettuce, onion, and cheese.
Top with a spoonful of pico de gallo and garnish with lime wedges.
To make the pico de gallo - Put all of the ingredients into a mixing bowl and stir it all together. Let sit for 15 minutes to allow the flavors to marry.