Combine the jalapeño, garlic, cilantro, citrus juices, vinegar, oil, soy sauce, cumin, salt, and pepper.
Marinate flank steak in the mixture for 1 to 4 hours in the refrigerator.
Preheat a barbecue grill or a pan on the stovetop to medium-high heat.
Take the steak out of the marinade and cook for 5 minutes per side.
Let the steak rest for 10 minutes before slicing against the grain.
Serve with lime wedges and tortillas, if desired.
