I make my own using:
1/4 cup red wine vinegar
1/4 cup canola oil
1 1/2 teaspoon cumin
1 teaspoon oregano
2 cloves of garlic, minced
Juice from one fresh lime
Splash of Worcestershire Sauce
Salt and pepper

I just marinate mine in garlic and lime juice. I chop up a little fresh cilantro to sprinkle on it after a quick stir fry on the meat. Also, saute the vegetables first, pull them from the skillet and then toss in the meat, don't crowd it, I usually do it in two batches. I get the skillet screaming hot before I toss in the meat, cook it quickly.