Marinade beef in food-safe plastic bag; turn steaks to coat, refrigerator for 15 minutes to 2 hours.
Remove steaks from marinade; discard marinade.
Place steaks on grid over medium, ash-covered coals.
Grill, covered, 10 to 14 minutes (over medium heat on preheated gas grill, 12 to 16 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally.
Combine avocado salsa ingredients in medium bowl. Set aside.
Warm tortillas and keep warm.
Carve steaks into slices.
Serve steak in tortillas with avocado salsa.
Top with onion, cilantro and lime wedges, as desired.