Mix beef with marinade sauce in a bowl. Stir well.
Place it in the refrigerator and let it rest for at least 1 hour.
Heat vegetable oil in a skillet.
Cook the beef together with the marinade sauce until browned and the marinade sauce reduced. Remove from the heat. Set aside.
Heat the tortillas. Arrange on a plate. Add beef, red onion, avocado and cilantro leaves. Squeeze some lime wedges.
Serve warm. Yum!