In a medium bowl, combine the sliced steak with 1 tablespoon of olive oil, salt, pepper, chili powder, cumin, smoked paprika, cayenne pepper (if using), minced garlic, lime juice, and Worcestershire sauce. Toss well to coat. Marinate for at least 15 minutes, or up to 4 hours in the refrigerator.
Heat 1 tablespoon of olive oil in a large, heavy skillet (cast iron works best) over medium-high heat until shimmering.
Add half of the marinated steak strips to the hot skillet in a single layer. Cook for 2 to 3 minutes per side until browned and cooked through. Remove the steak from the skillet and set aside.
Add the remaining steak to the skillet and cook in batches if necessary to avoid crowding, which prevents browning. Remove the cooked steak and set aside with the first batch.
Add the sliced onions and bell peppers to the same skillet. Cook, stirring occasionally, for 5 to 7 minutes until the vegetables are tender-crisp and slightly charred.
Return all the cooked steak to the skillet with the vegetables. Toss everything together for 1 minute to reheat the steak and combine the flavors.
Serve immediately with warm tortillas and your choice of toppings.
Notes
For the best ‘sizzling’ effect, use a cast iron skillet and make sure it is very hot before adding the steak.
If you prefer a less intense flavor, reduce the chili powder to 2 teaspoons.
You can substitute flank steak with skirt steak for a slightly richer flavor.