Prepare the Marinade: In a medium bowl, whisk together the olive oil, lemon juice, minced garlic, rosemary, thyme, Dijon mustard, salt, and pepper.
Marinate the Chicken: Place the chicken breasts in a resealable plastic bag or shallow dish. Pour the marinade over the chicken, making sure it's evenly coated. Seal the bag or cover the dish with plastic wrap. Refrigerate for 2-4 hours, turning the chicken occasionally.
Grill or Bake the Chicken:
Grill: Preheat your grill to medium-high heat. Remove the chicken from the marinade and grill for 6-7 minutes on each side, or until the internal temperature reaches 165°F.
Bake: Preheat your oven to 375°F. Place the marinated chicken on a baking sheet and bake for 25-30 minutes, or until the internal temperature reaches 165°F.
Serve: Let the chicken rest for 5 minutes before serving. Garnish with additional fresh herbs if desired.