In a medium bowl, whisk together the vinegar, soy sauce, 4 cloves of garlic, juice of two limes, and olive oil. Season with salt, black pepper, white pepper, garlic powder, chili powder, oregano, cumin and paprika. Whisk until well blended, then pour over the steak. Cover, refrigerate for 1-8 hours.
Remove from marinade and slice the flank steak with the grain in half.
Skewer the bell peppers and onions like a kebob.
Wrap the tortilla shells in foil.
Mix the fajita seasoning and vegetable oil right before putting the vegetables on the grill to avoid it getting too thick.
Grill the peppers and onions over preheated medium high grill, basting periodically with fajita/oil mixture until charred and vegetables are crisp tender. Approx 10-15 minutes.
Move vegetables to a cool part of the grill and place steak over hottest part of the grill. Grill 3-5 minutes per side or until steak is medium. At the same time, place the tortilla packet on the grill. Turn the tortilla packet every few minutes to avoid burning the tortillas.
Allow the steak to rest for at least 5 minutes before slicing thinly against the grain.
While the steak is resting, remove the onions and peppers from skewers and chop into bite size pieces.
Build your fajitas and enjoy! Great with guacamole and sour cream.