I made a chimchurri sauce/relish this weekend to serve with some nice NY strips. It was awesome, and is even better after a few days.
Here's how I made it (based on ingredients I had on hand):
4 tb olive oil
4 tb red wine vinegar
4 tb beef stock
1 cup parsley - chopped super fine
5 big cloves garlic - chopped super fine
1/2 large red onion - chopped super fine
a hefty dose of red chili flakes
salt to taste
You just mix it all up. No cooking. I put it in a mason jar in the fridge and we just use it as we need it. It was really good . . halfway between a pesto and a pico de gallo. Last night we were too tired to cook anything, so we just grilled up some hamburger patties to have with a garden salad . . the chimchurri on simple hamburger patties was pretty damn awesome.
I think authentic versions use scallion instead of onion and has a bunch of fresh oregano, too . . but I didn't have that on hand.