There are many different ways to make these little tacos that you can buy from street vendors in both Mexico and the US. I'm lucky enough to have a couple different trucks within walking distance of work and buy my lunch there every week or so. I watched how they cooked it and have tried different recipes on my own. This is just one but I think it works out alright.
I'm cooking for two so you can scale this however you need for the number you have around.
1 lb asada (skirt steak) I've tried other cuts but but found this is by far the best choice for tacos.
Marinade:
8 oz orange juice
1 packet of Sazon Goya
1 tsp cumin
1 tsp fine minced garlic (fresh or jar)
2 T fine chopped fresh cilantro
Juice from one or two small limes
I put the asada and marinade in a large freezer bag so the the meat is completely covered then put it in the refrigerator. I let it marinate for 3 days or so, mixing it up every 24 hrs.
I cook the meat in two stages. The first time I grill the asada to rare and then let it cool off. Then I slice it into thin strips and put those back in the fridge for a few hours. I find it is easier to fine dice the meat when it is cold but YMMV.
When I've got the meat fine diced I grill it along with some freshly diced yellow onion, and a serrano or jalapeno pepper. Add some thin sliced radishes, hot sauce of your choice, and a dab of crema and you're good to go. Traditionally served on two small white corn tortillas that you can grill to soften them but I just do it in a taco steamer in the microwave.