Season steaks with salt and pepper and set aside until ready to grill to desired temperature.
Combine the vinegar, garlic, shallot and a generous pinch of salt in a blender and blend on low until smooth. Add the parsley, cilantro, oregano, chili flakes and blend on medium speed. With the blender running, slowly drizzle in the olive oil and puree until smooth, about 1 minute, stopping to scrape down the sides if necessary. Season the chimichurri with more salt and pepper and transfer to a serving bowl, cover with plastic and refrigerate until ready to serve.
When steaks are cooked to temperature place on a platter and drizzle the chimichurri sauce on top of grilled steaks and serve.
