1. In a medium bowl, mix the oil, soy sauce, vinegar, lemon juice, Worcestershire sauce, mustard, garlic, and ground black pepper. Place meat in a shallow glass dish. Pour marinade over the steak, turning meat to coat thoroughly. Cover, and refrigerate for 6 hours.
2. Preheat grill for medium-high heat.
3. Oil the grill grate. Place steaks on the grill, and discard the marinade. Grill meat for 5 minutes per side, or to desired doneness.
My Note: I would suggest that you let the meat reach room temperature before grilling rather than cooking it straight out of the refrigerator as the recipe suggests. It makes for a more tender steak. Sometime I do mine in the oven. I like to serve flank steak with a sauce and if you pour the marinade over the steak before roasting you are left with an awesome gravy that is great over potatoes too! Also, marinating overnight is great, but you should try this even if you only have an hour to marinate.
This marinade is use to making grilled flank steak for fajitas! I did make a couple of additions. Since we were using it for fajitas I added 1/2 T. ground Coriander and 1/2 T. ground Cumin. For the vinigar I used Balsamic. We left the steak in a zip lock for 2 days and when we sliced it, it could have been cut with a fork! And sometime I cooked this in my broiler for 8 minutes on each side, basting occasionally with marinade. It was medium rare and quite good. Nice way to tenderize a tougher piece of meat.
This was my son second time making this recipe for steak fajitas. This time, he added 1.5 teaspoons of ground cumin and corriander, along with a small handful of cilantro leaves, then substituted fresh lime juice and added a little lime zest. This time there were no complaints of bland steak, and the fajitas were a big hit! This is a great way to make fajitas, my son never thought to bbq a flank steak before. He marinated the meat for 48 hours (and added some slices of sweet onion, red and yellow pepper to the marinade an hour before he was ready to grill). He put the vegetables in tin foil and cooked them on the bbq as well (they took longer than the steak which he cooked to medium) We sliced the meat into thin strips with an electric knife and served with the vegetables, tortillas, cheese, sour cream, salsa, and guacamole. They were awesome! Not bad for 15 yr. old. Be sure to marinade for the FULL TIME given in recipe. Otherwise, the taste may not come out right. Good as leftovers the next day too! I have even used this with chicken. I've also cooked a roast in the slow cooker with this. I am addicted to it!