Here's a similar dish, and for me, the original of what I toyed with above:
my variation of chimichurri includes: minced parsley, red onions (preferable to white, but white also work), diced garlic (I use store bought in a jar), oregano, cayenne pepper, pepper, salt, red wine vinegar, olive oil. shake it up real good, then refrigerate for about 5 hours before serving. Keep refrigerated and it'll be good through the next day.
I've been to argentina and had a few versions of it, but I'm particular to my own (which was a recipe given to our family from a siblings' argentinian soccer trainers). works with steak / lamb / chicken / fish, salads, on black beans, etc.. I'll be mixing the remnants in with black beans for my Game of Thrones meal tonight