Combine lime juice, olive oil, minced garlic, cumin, salt, and pepper, then coat the flank or skirt steak evenly. Marinate for 30 minutes at room temperature or in the refrigerator until ready to grill, with the steak fully submerged in the marinade.

Preheat the grill to high heat until hot. Grill the steak for 4-5 minutes per side for medium-rare, leaving clear char marks on the surface.

Transfer the steak to a plate and let it rest for 10 minutes so juices redistribute. Slice thinly against the grain once rested to keep each bite tender.

Gently mix diced avocados, diced cherry tomatoes, diced red onion, chopped cilantro, lime juice, and salt. Stir just until combined so the avocado stays chunky.

Warm corn tortillas on the grill until pliable and lightly charred. Assemble street tacos by layering warm tortillas with sliced steak and spooning on the avocado salsa, serving with lime wedges.