1 Tbsp vegetable oil
1 lb of flank grass fed steak, skirt steak or carne asada
1 large yellow onion, peeled and sliced with the grain, not against the grain as one would normally slice an onion. Slice first in half, and then slice off sections a half inch wide at widest point.
2-3 bell peppers of various colors, stemmed, seeded, de-ribbed, sliced lengthwise into strips
Salt
Marinade
Juice of 1 lime
2 Tablespoons of olive oil
2 cloves garlic, peeled, minced
1/2 teaspoon ground cumin
1/2 fresh Jalapeño pepper, seeded, ribs removed, finely chopped
(be careful not to touch your eyes or anywhere near your eyes after handling a Jalapeño pepper!)
1/4 cup chopped fresh cilantro, including stems 
Preparation
Mix all marinade ingredients. Coat the steak with the marinade and let it sit at room temperature for an hour, or longer in the fridge.
Before you cook the meat, wipe off most of the marinade and sprinkle the steak with salt.
Set a large cast iron pan or griddle over high heat and let this heat up for 1-2 minutes. Add the tablespoon of oil to the pan and let this heat up for 1 minute.
Add the steak, frying on each side for 3 minutes, or to desired doneness. 3 minutes per side will yield approximately medium rare doneness for an average cut of flank steak. Carne asada and skirt steak will need less time.
If the pan starts to smoke too much, reduce the heat to medium-high. You want the steak browned, not burned. Remove from pan and let sit, tented with foil, for 5 minutes.
Cook the vegetables while the meat is resting. Add a little more oil to the pan if necessary, then add the onions and bell peppers.
Let these sear for 1 minute before stirring, then stir every 90 seconds or so as the veggies sear. Cook for 5-6 minutes total.
Slice the meat against the grain into thin slices. If you slice the meat at an angle, you will be able to get your slices pretty thin. These cuts of steak are flavorful but can be a little tough, so thin slices will really help make it easier to eat.
Serve immediately with shredded cheese, salsa, shredded iceberg lettuce, sour cream, guacamole and warm flour tortillas.
(Hint for warming tortillas – put in microwave over a paper towel for 20 seconds on high heat.)
