Mix together olive oil, lime juice, spice mix, and garlic, then transfer to a freezer bag. Add the steak and seal the bag tightly, pressing out as much air as possible. Refrigerate the steak for at least 30 minutes and up to 8 hours.

Wash the bell peppers, peel the onion, and slice both into very thin strips. Peel and finely dice the garlic. Wash the jalapeño, halve it, and slice it into strips.

Heat a pan over medium-high heat. Add the beef steak and sear on both sides for about 2 to 3 minutes. Remove the steak from the pan, place it on a plate, and cover it with aluminum foil.

Add oil, bell pepper and onion strips to the pan and fry over medium-high heat with a generous pinch of salt for about 5 minutes.

Once the bell pepper strips are nice and soft and the onions are translucent, reduce the heat slightly and add the garlic, jalapeño, spice mix, and the juice of half a lime. Sauté over medium heat for another five minutes.

Meanwhile, slice the steak into thin strips. Return the beef strips to the pan and fry over medium heat for about one to three minutes, until they reach the desired degree of doneness.

Season the fajita pan with salt, pepper and, if necessary, a little chili or lime juice, and serve with side dishes of your choice.