Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Slice the flank steak against the grain into thin strips, approximately 2 inches in length, to ensure the meat remains tender after roasting.
Core the red and green bell peppers and slice them into thin strips, then thinly wedge the red onion.
In a large mixing bowl, combine the steak strips, bell peppers, and onion wedges.
Drizzle the extra virgin olive oil over the mixture and sprinkle with sea salt, black pepper, garlic powder, and smoked paprika.
Toss everything together with your hands or tongs until the beef and vegetables are thoroughly and evenly coated with the oil and spices.
Spread the mixture in a single, even layer onto the prepared baking sheet, making sure not to overcrowd the pan so the ingredients roast properly.
Roast for 12-15 minutes, or until the beef is cooked to your desired level of doneness and the peppers have developed slightly charred, caramelized edges.
Remove from the oven and let the beef rest on the pan for 2 minutes before serving to allow the juices to settle.