Pat the flank steak dry with paper towels and season both sides evenly with sea salt, black pepper, garlic powder, and smoked paprika.
Preheat a grill or grill pan over medium-high heat and lightly brush the surface with the extra virgin olive oil.
Place the steak on the grill and cook for 4 to 5 minutes per side for medium-rare, then transfer to a cutting board to rest for 5 minutes.
While the meat rests, thinly slice the radishes, finely dice the red onion, and slice the avocado into thin wedges.
Briefly place the corn tortillas on the grill for 30 seconds per side until they are warm and pliable with light char marks.
Slice the rested flank steak against the grain into thin strips to ensure maximum tenderness.
Assemble the tacos by dividing the steak strips between the two tortillas, then topping with avocado, radishes, and red onion.
Garnish with fresh cilantro and a generous squeeze of lime juice before serving immediately.