Combine everything but the olive oil in a food processor. Blend until chopped, then add olive oil, and continue blending until combined.
Place a drip tray underneath where the chicken will be roasting, to prevent flare-ups from burning the chicken. Also place a tinfoil covered brick on the barbecue.
Preheat barbecue on high heat for about 10 minutes.
While the barbecue is preheating, spatchcock your chicken, and rub with about 3/4 of the chimichurri, saving some to put on the chicken after cooking.
Once the barbecue has preheated, turn burners down to medium, place chicken skin-side up on grill, placed brick on chicken, and cook for about 45 minutes to an hour, turning once halfway through, or until the chicken registers 165F in the breast, then remove and allow to rest for ten minutes.
Spread the rest of the chimichurri on the chicken, and serve!