Combine the garlic, lime juice, vinegar, and red pepper in a large resealable plastic bag. Prick the steak all over with a fork and add to the marinade; turn to coat. Refrigerate for at least 1 hour and up to 4 hours.
Heat grill to medium-high. Once it's hot, clean the grill grate with a wire brush. Just before grilling, oil the grill grate.
Season the steaks with ¾ teaspoon each salt and black pepper. Grill, turning once, until an instant-read thermometer inserted into the thickest part registers 130° F, 6 to 8 minutes for medium-rare. Let rest for 10 minutes before thinly slicing against the grain.
Divide the steak among the tortillas and top with the Avocado-Lime Salsa.
* Total Time includes marinating