In a bowl, whisk together the grapeseed oil, parsley, vinegar, jalapenos, chile flakes, garlic, lime juice and 2 teaspoons each salt and pepper. Set aside 1/2 cup of the chimichurri sauce for marinating the steak; reserve the remaining sauce for serving.
Tenderize the skirt steak by pounding it lightly. Sprinkle the steak with kosher salt and black pepper, keeping in mind that there is salt and pepper in the marinade. Transfer to a bowl or dish and add the 1/2 cup chimichurri sauce. Marinate, refrigerated, at least 10 hours or overnight.
When ready to cook the steak, heat a grill or saute pan to medium heat. Remove the steak from the marinade (discard the marinade). Grill the steak to medium-rare, 4 to 5 minutes per side, or cook to desired temperature or doneness. Let the steak rest for 5 minutes before slicing in thin strips on the bias.
Put some steak slices on each plate and spoon over the reserved chimichurri. Serve with roasted carrots and roasted yucca or your favorite vegetable and starch. Enjoy!