Finely chop the garlic cloves (or crush them with a garlic crusher) and transfer to a large bowl.
Chop the cilantro and jalapeno finely as well and add to the bowl. (WEAR GLOVES when chopping the jalapeno! If you like some extra heat, leave the seeds in. If not, carefully remove the seeds with your knife)
Juice the lime and the orange and pour in to the bowl.
Pour in the vegetable oil and mix the marinade with a fork or whisk.
On a tray that's long enough for your skirt/flank steak to lay flat, place your beef on it and season with salt and pepper.
Spoon over the marinade and don't be afraid to rub it in with your hands. (You can wear gloves if you prefer)
Once the steak is coated on both sides, cover the tray with some plastic wrap and put in the fridge for 4 hours. (Or overnight for incredible flavor!)
When you're ready to start cooking, take the steak out of the fridge and wait for it to come to room temperature.
Heat up a large shallow saucepan or cast iron skillet on medium/high heat. If you feel like grilling it for some added smoky taste, go right ahead and fire up your grill or BBQ!)
Since the beef has been marinating in vegetable oil among other ingredients, you don't need to add any excess oil to the pan. Once the pan is hot, carefully lay the steak in away from you to avoid splatter)
You should hear an instant sizzle! Cook each side for 5-7 mins on each side until the middle is pink. (If you like your steak well done, cook for 10-12 mins on each side or until the inside is brown)
Once the beef is cooked, lay on a chopping board or tray and cover with aluminium foil. Leave to to rest for at least 10 mins)
After 10 mins, remove the foil and slice the beef against the grain.
If you want to add this to a burrito or taco, or if you have kids eating this, chop the slices into smaller bitesize cubes like in the image above) Enjoy!