Pat the flank steak dry with paper towels and rub both sides evenly with chili powder, cumin, garlic powder, sea salt, and black pepper.
Heat half of the olive oil in a large cast-iron skillet over medium-high heat until the oil is shimmering.
Place the steak in the hot skillet and sear for 4-5 minutes per side for medium-rare, then transfer to a cutting board to rest for at least 5 minutes.
While the steak rests, use a vegetable peeler to slice the zucchinis into thin, wide ribbons, stopping when you reach the seeds.
Wipe out the skillet and add the remaining olive oil over medium heat.
Sauté the zucchini ribbons for 2-3 minutes until just tender, then squeeze the juice of half the lime over them and toss with fresh cilantro.
Slice the rested steak against the grain into thin strips and serve immediately over the zucchini ribbons with the remaining lime wedges.