Prepare the Marinade: In a bowl, whisk together Dijon mustard, olive oil, minced garlic, rosemary, thyme, salt, pepper, and lemon juice.
Marinate the Chicken: Place the chicken breasts in a resealable plastic bag or shallow dish. Pour the marinade over the chicken, ensuring it’s well-coated. Refrigerate for at least 30 minutes, or up to 4 hours for more flavor.
Cook the Chicken: Preheat the grill or a skillet over medium-high heat. Remove chicken from the marinade and discard the remaining marinade. Grill or cook the chicken for about 6-7 minutes on each side, or until fully cooked and the internal temperature reaches 165°F (74°C).
Serve: Let the chicken rest for a few minutes before slicing. Serve warm with your choice of sides.