Combine the parsley, garlic, olive oil, and red wine vinegar in a blender or food processor. Blend until it reaches your desired texture.
Reserve a portion of the chimichurri sauce for serving. Marinate the chicken breasts in the remaining chimichurri for at least 30 minutes, or up to overnight in the refrigerator.
Preheat the grill or oven. Cook the chicken until it reaches an internal temperature of 165 degrees Fahrenheit, approximately 6-7 minutes per side on the grill or 20-25 minutes in the oven at 375 degrees Fahrenheit.
Serve the chicken with the reserved chimichurri sauce.
Notes
Make sure the chicken breasts are evenly thick for consistent cooking.
For a smoother chimichurri, blend the ingredients longer, but if you prefer a chunkier texture, reduce the blending time.
Let the chicken marinate in the chimichurri for at least 30 minutes to fully absorb the flavors.
Don't overcook the chicken. Use a meat thermometer to ensure it reaches an internal temperature of 165 degrees Fahrenheit.
Leftover chimichurri sauce can be stored in the refrigerator for up to a week and used in other dishes.