Slice the flank steak against the grain into thin strips. In a bowl, combine lime juice, chili powder, cumin, paprika, garlic powder, onion powder, salt, and black pepper. Add the steak strips to the marinade, ensuring they are well coated, then cover and refrigerate for at least 30 minutes, or up to 2 hours.

Heat olive oil in a large skillet or cast-iron pan over medium-high heat. Once hot, add the marinated steak in a single layer, cooking for 2-3 minutes per side until seared and cooked to your desired doneness. Remove the steak from the pan and set aside, covering to keep warm.

In the same skillet, add the sliced bell peppers and onion. Sauté for 5-7 minutes, stirring occasionally, until vegetables are tender-crisp. Return the cooked steak to the skillet with the vegetables and toss to combine, heating through for about 1 minute.

Serve the steak fajitas immediately with warm tortillas, sour cream, and salsa, or your favorite toppings.