In a bowl combine garlic, jalapeno, cilantro, lime juice, vinegar, salt, cumin, chili powder and olive oil. Whisk to combine. Place steak in a shallow dish. Pour marinade over steak and marinate for at least 2 hours but not more than 8.
When you are ready to cook the steak, preheat oven broiler. Place steak on a baking sheet. Cook steak 8 - 10 minutes. Use tongs to turn over (you don't want to pierce it with a fork it will release the juices) and cook another 8 minutes. Remove from oven, allow to rest for 10 minutes before slicing thinly against the grain.
While the steak is resting cook your tortillas. Heat a thin layer of oil in a skillet. Cook tortillas one at a time for 30 seconds on each side and then fold over to form taco shell. Transfer to a paper towel lined plate.
To assemble the taco, place a few slices of meat on the taco shell. Top with lettuce, tomato, cojita cheese and avocado. Serve.