Grilled steak tacos get a spicy salsa marinade and are topped with tequila-kissed pickled red onions.
To prepare Salsa, place yellow onion slices on grid over medium, ash-covered coals. Grill onion, covered, 12 to 14 minutes (over medium heat on preheated gas grill, covered, 12 to 14 minutes), turning occasionally. Roughly chop grilled onion; set aside to cool.
Combine grilled onion, cilantro, chipotle peppers, garlic, black pepper and 1/2 teaspoon salt in blender container. Cover; pulse on and off until pureed. With blender running, slowly add oil to blender through opening in cover, processing until smooth. Reserve 1 cup salsa; cover and refrigerate.
Place beef steaks and remaining salsa in food-safe plastic bag; turn steak to coat. Close bag securely and marinate in refrigerator 30 minutes.
Remove steaks from marinade; discard marinade. Pat steaks dry with paper towel; season with salt, if desired.
Grill, covered, 10 to 14 minutes (over medium heat on preheated gas grill, covered, 12 to 16 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally. Keep warm.
Place Cotija cheese and queso fresco in food processor container. Pulse on and off until cheese resembles coarse breadcrumbs. Cover and refrigerate until ready to use.
Carve steaks lengthwise into 1 inch strips, then across the grain into 1/2-inch pieces. Divide beef among tortillas; top with reserved 1 cup salsa, pickled onions, cheese, avocado, cilantro and lime wedges, as desired.