Marinate the flank steak with olive oil, salt, pepper, chili powder, and cumin for at least 30 minutes.
Preheat a grill or skillet over medium-high heat.
Cook the flank steak for about 5 minutes on each side or until it reaches your desired doneness.
Remove the steak from the heat and let it rest for 5 minutes.
While the steak is resting, warm the corn tortillas on the grill for about 30 seconds on each side.
Slice the steak thinly against the grain.
Assemble the tacos by placing sliced steak on each tortilla.
Top with corn salsa and avocado slices.
Garnish with fresh cilantro.
Serve with lime wedges on the side.