01 - In a medium bowl, whisk together the fresh orange juice, orange zest, Dijon mustard, olive oil, honey, minced garlic, dried thyme, salt, and black pepper until thoroughly combined.
02 - Place the chicken breasts in a large resealable plastic bag or shallow dish. Pour the marinade over the chicken, ensuring all pieces are evenly coated. Seal tightly and refrigerate for at least 1 hour, or up to 8 hours for deeper flavor penetration.
03 - Preheat the grill to medium-high heat. Lightly oil the grill grates to prevent the chicken from sticking during cooking.
04 - Remove the chicken from the marinade, shaking off any excess. Discard the used marinade. Grill the chicken for 6 to 7 minutes per side, or until the internal temperature reaches 165°F and the meat is no longer pink in the center.
05 - Transfer the grilled chicken to a cutting board and let it rest for 5 minutes before slicing. Garnish with fresh orange slices and chopped parsley if desired, then serve immediately.