Thin Beef with Onions & Jalapenos

OK - so most of the recipes I post here are ultra cheap so I should caveat that this one is slightly more expensive.

I was at my local butcher shop and saw thinly sliced beef was selling for $2.99 a pound so I bought a couple of pounds..

This was really an experiment and turned out to have delightful results.

Ingredients
1 jalapeno
2 medium yellow onions
1 pound thinly sliced beef
Half a cup of vinegar
Salt, Pepper
teaspoon adobo
teaspoon cumin
One garlic clove finely diced (optional)
Half a cup of water (if needed)
One tablespoon olive oil

Directions:
Dice both onions and split them in 2 equal parts.
Take the beef and marinate with one one part of the onions, vinegar, salt, pepper, cumin, adobo, garlic if you like. Add the water if it seems dry. Basically you want some liquid in the marinade once the beef is all coated. The beef should marinate for at least an hour.
Take the jalapeno and char it on an open flame or in a saucepan with no oil.
Once you have a good char (but not burnt fully), take the jalapeno off the flame and set aside to cool off.
Once you can handle the jalapeno, cut it in half and get rid of the seeds and rib and then dice the jalapeno finely and set aside.
Wash your hands well now so you don't burn yourself with the jalapeno juice.
Once the beef is marinated, put a skillet on medium high with a tablespoon of oil.
Add your finely diced onion that you had set aside in the beginning.
Once the onions turn translucent, add the jalapenos and let them cook for a minute more.
Now add the beef along with the juices from the marinade.
Cook on medium for about 8 minutes flipping the beef often so that it isn't overly well on any side.
The marinade should have reduced considerably and the beef should be medium well..

I serve this with toast and it yielded 4 servings for me.