In a large mixing bowl combine orange juice, garlic powder, cumin, and Worcestershire sauce. Slice the skirt steak very thin lengthwise and then again in the opposite direction so that your pieces are about 2 inches long.
Place the sliced steak into the bowl with the marinade. Allow the steak to marinade for at least 1 hour.
Heat a large skillet to medium heat. Remove the steak from the marinade and place into the pan and sear, turning at least once, until the steak is cooked through and no longer pink.
Heat a separate pan to medium heat on the stovetop for the tortillas. Place a tortilla in the preheated pan and cook for 30 seconds on each side. Repeat with the remaining tortillas.
Prepare the tacos by taking a warm tortilla and filling them with the meat and then topping with diced onion and avocado. Sprinkle cilantro on the top. Serve with lime wedges for squeezing over the top of the tacos.