Place parsley, oregano, garlic, vinegar, red pepper flakes, and salt in a food processor and pulse until finely chopped; scrape down the sides of the bowl as needed. With the motor running, add oil in a steady stream. Measure out ½ cup of sauce and transfer the remaining sauce to an airtight container and refrigerate at least 2 hours or up to 1 day to allow the flavors to meld. (The chimichurri will keep in the refrigerator for up to 1 week.)
Using a sharp chef’s knife, roll cut the tenderloin. Start by placing the tenderloin on a cutting board with and end toward you. Take your knife and begin cutting along the side, parallel to the cutting board about ½-inch above the board. As you cut, "unroll" the tenderloin.... kind of like unrolling a roll of paper towels. Once you have unrolled the meat, place it between two sheets of plastic wrap and pound ¼-inch thick. Add half of the reserved chimichurri to a large baking dish and place the meat in the pan and pour the remaining chimichurri over the meat and rub the sauce into both sides of the meat. Cover and let marinate in the refrigerator overnight, turning occasionally.
Set up grill for direct high heat. Brush and oil grates before cooking.
Remove meat and reserved chimichurri sauce from the refrigerator. Stir and taste chimichurri and adjust seasoning, if necessary. Remove meat from marinade and pat dry with paper towels. Season both sides liberally with salt and pepper. Place on grill and for about 4 to 5 minutes for medium-rare meat; let rest for 5 minutes before slicing.
Slice meat on the bias (angle knife 45 degrees to the board) and against the grain of the meat for nice wide strips of meat. Serve hot with flour tortillas heated on the grill and extra chimichurri on the side.
Recipe by Grilling Outdoor Recipes powered by Bull Outdoor Products at http://www.grillingoutdoorrecipes.com/churrasco-steak-with-chimichurri/