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 black pepper. Rub this mixture all over the flank steak.
Place the seasoned steak on the grill and cook for about 4-5 minutes on each side for medium-rare, or until it reaches your desired doneness. Remove from the grill and let it rest for 5-10 minutes.
While the steak is resting, prepare the avocado salsa by combining the diced avocados, tomato, red onion, cilantro, lime juice, salt, and pepper in a bowl. Gently mix until well combined.
Warm the corn tortillas on the grill for about 30 seconds on each side or until pliable.
Slice the rested steak against the grain into thin strips.
Assemble the tacos by placing a few strips of steak on each tortilla and topping with the avocado salsa. Serve immediately.