Preheat your grill or skillet over medium-high heat.
Season the flank steak with cumin, chili powder, salt, and pepper.
Drizzle olive oil on the grill or skillet.
Cook the steak for about 5-7 minutes on each side for medium-rare.
Remove the steak from heat and let it rest for 5 minutes.
While the steak rests, warm the corn tortillas in a dry skillet.
Slice the steak thinly against the grain.
Assemble the tacos by placing steak slices on tortillas.
Top with diced tomatoes, onions, and cilantro.
Squeeze lime juice over the assembled tacos before serving.