Preheat your oven to 400°F (200°C) and line a small baking sheet with parchment paper.
In a small mixing bowl, whisk together the lime juice, half of the olive oil, chili powder, smoked paprika, garlic powder, onion powder, sea salt, and black pepper.
Rub the spice marinade thoroughly over both sides of the flank steak and let it marinate at room temperature for 10 minutes.
Toss the sliced bell peppers with the remaining olive oil on the prepared baking sheet and spread them in a single layer.
Heat a cast-iron skillet over medium-high heat until very hot, then sear the steak for 3-4 minutes per side for a perfect medium-rare.
While the steak is searing, place the bell peppers in the oven and roast for 10-12 minutes until they are tender and slightly charred.
Transfer the steak to a cutting board and allow it to rest for at least 5 minutes to lock in the juices.
Thinly slice the steak against the grain and serve immediately topped with the roasted peppers.