In a large mixing bowl, combine sliced flank steak, peppers, red onion, olive oil, cumin, chili powder, cayenne, and red pepper flakes.
Generously season with salt and pepper, to taste, and mix until everything is well coated.
Spread the steak and pepper mixture in a single layer onto the prepared baking sheet and roast in pre-heated oven for 15-20 minutes.
Remove sheet pan from oven and sprinkle with fresh cilantro and a squeeze of fresh lime juice.