In a medium bowl, whisk together the olive oil, soy sauce, apple cider vinegar, honey, and Dijon mustard until well combined.
Add the minced garlic, dried oregano, dried thyme, black pepper, salt, and red pepper flakes (if using) to the bowl. Whisk until all ingredients are fully incorporated.
Place your chicken (about 2 pounds of boneless, skinless chicken breasts or thighs) in a large resealable plastic bag or a shallow dish.
Pour the marinade over the chicken, ensuring it is fully coated. Seal the bag or cover the dish and refrigerate for at least 1 hour, or up to 8 hours for maximum flavor.
Preheat your grill to medium-high heat. Remove the chicken from the marinade and discard the marinade.
Grill the chicken for 6-7 minutes on each side, or until the internal temperature reaches 165°F.
Remove the chicken from the grill and let it rest for 5 minutes before slicing and serving.