Trim the outer fat, or ask the butcher to do so.
Combine the soy sauce, lemon juice, oil, cumin, cayenne, scallions, jalapeno, garlic, and pepper in a glass or ceramic bowl. Put the steaks in a glass or ceramic dish and pour the marinade over the meat. Cover and marinate at room temperature for 30 minutes or refrigerate for as long as 2 hours. Turn the meat once or twice and return to room temperature if refrigerated before grilling.
Prepare a charcoal or gas grill. Lightly spray the grill rack with vegetable oil cooking spray. The coals should be moderately hot to hot.
Lift the steak from the marinade. Discard the marinade. Grill the steak, covered, for 10 to 12 minutes. Turn and grill, covered, for 10 to 12 minutes longer for medium rare, or until it reaches the desired degree of doneness. Let the meat rest for a few minutes before carving. Transfer to a warmed serving platter.