In a food processor, add shallot, garlic, and red wine vinegar. Pulse until roughly chopped. Stop and scrape down the sides. Add oregano, parsley, and basil. Slowly add olive oil while pulsing. Stop and scrape down the sides once more. You may stop pulsing when herbs are finely chopped. Stir in salt, pepper, and red pepper flakes.

Place chicken breasts in a bowl or resealable plastic bag with half of the chimichurri sauce. Place in the refrigerator and marinade for 1 hour or up to 24 hours.

Heat an outdoor grill to medium heat. Add the chicken in a single layer so they are not overlapping each other.

Cook chicken for 6-8 minutes per side, or until a thermometer inserted into the thickest part of the chicken registers 165 degrees F.

Let chicken rest for 5 minutes. Drizzle remaining chimichurri sauce on top of chicken, slice and serve.