Unroll the flank steak and lay it in a large glass baking dish.
In a medium bowl, whisk together the olive oil, lime juice, soy sauce, vinegar, and minced garlic.
To this mixture, add the paprika, cumin, oregano, chili powder, garlic powder, black pepper, white pepper, and salt.
Whisk until well blended, then pour over the steak. Cover the dish with plastic wrap, and marinate for 1 to 8 hours, turning steak halfway through.
Chop the onions and peppers and sauté in 2 tablespoons olive oil until soft and golden brown. Remove from heat and set aside.
Preheat grill to medium heat. Remove bowl containing steak from refrigerator and allow to stand at room temperature for 30 minutes.
Remove steak from marinade and place on grill over direct heat for 5 minutes. Turn steak and cook another 4 minutes. Wrap steak in aluminum foil and allow to rest 7-8 minutes before slicing against the grain.
Serve on tortillas, topped with peppers, onions, and crema (if desired).