Prepare the veggies on a separate plate so they are ready when you need them.
3 small bell pepper, 1 brown onion
Mix all the marinade ingredients in a large shallow dish (or ziplock bag). Reserve 2 tablespoons for the veggies later.
2 teaspoon lime juice and more for serving, 1 ½ teaspoon cumin, 1 teaspoon smoked paprika, 2 large garlic cloves, ½ teaspoon salt, ¼ teaspoon black ground pepper or less/to taste, 1 tablespoon olive oil, ¼ teaspoon chili flakes
Coat the steak with the marinade and allow to marinate for 30 minutes or for a couple of hours (refrigerated) if you have time. Before cooking allow steak come to room temperature.
1 pound sirloin
Heat a good cast iron skillet or grill pan over medium-high heat with some vegetable oil. Sear the steak for 4 minutes on both sides (to achieve medium rare)* and 1 minute on both sides/edges (kitchen thongs will be very helpful here to hold the steak!).
vegetable oil for cooking
Transfer to cutting board, sprinkle with sea salt, and let rest for 5 minutes. Cut into at least ½ inch strips to serve.
Wipe the skillet and add more vegetable oil. Cook the veggies on medium high with 2 tablespoons of marinade until just softened. Season with salt and pepper in the end.