To cut steak into thin strips, place the steak in the freezer (not necessary to make recipe, it just makes it easier to slice) for 20-30 minutes then use a sharp knife to slice the steak thinly AGAINST the grain. Place the strips of steak in a glass bowl and add the lime juice, salt, cumin, and garlic. Coat steak and let sit for 15-20 minutes.
Meanwhile prepare the peppers and onions by heating up a large skillet over medium high heat. Once the skillet is hot place the peppers and onions in and let sit till they begin to caramelize and slightly blacken. Stir and caramelize on the other sides. Remove to a plate to keep warm.
In the same skillet toss in the steak strips and and stir occasionally till the beef is cooked to your liking.
Serve the peppers, onions and steak on soft flour tortillas with your desired toppings. Enjoy!
Make sure your skillet is nice and hot before cooking the peppers so they have a chance to sear and get a little charred. If not, they'll just steam and get soggy.