To prepare the dinner, start by making the chimichurri a bit in advance to marinate the chicken. In a food processor, blend the herbs, garlic, onion, vinegar, and oil until smooth.
Reserve half of the sauce for dipping and marinate the chicken in the remaining sauce. Pot holes in the chicken with a fork to allow the marinade to penetrate the chicken.
For the potatoes, peel, and cut into slices. Boil for 8 minutes, remove, and run cool water over the potatoes. Pat dry and brush with oil.