Marinate the flank steak in olive oil, garlic, cumin, chili powder, salt, and pepper for at least 30 minutes.
Preheat your grill or skillet over medium-high heat.
Remove the steak from the marinade and let excess oil drip off.
Grill the steak for about 5 minutes per side, or until desired doneness.
Remove the steak and let it rest for 5 minutes.
Warm the corn tortillas on the grill for about 30 seconds on each side.
Slice the steak against the grain into thin strips.
Assemble the tacos by placing steak slices in the tortillas.
Top with avocado, pico de gallo, and red onion.
Garnish with fresh cilantro before serving.