Preheat your grill to medium-high heat.
In a small bowl, mix together the olive oil, chili powder, cumin, garlic powder, onion powder, salt, and pepper. Rub this mixture all over the flank steak.
Place the seasoned steak on the grill and cook for about 5-7 minutes per side for medium-rare, or until it reaches your desired doneness. Remove from the grill and let it rest for 5 minutes before slicing.
While the steak is resting, prepare the avocado salsa. In a medium bowl, combine the diced avocados, tomato, red onion, cilantro, lime juice, and salt. Gently mix until well combined.
Warm the corn tortillas on the grill for about 30 seconds on each side.
Slice the rested steak against the grain into thin strips.
To assemble the tacos, place a few slices of steak on each tortilla and top with the avocado salsa. Serve immediately.