Steps
1. In a small bowl, mix together soy sauce, balsamic vinegar, garlic, honey, mustard, pepper, and onion powder until blended. 2. Place duck breast in a large resealable plastic bag and pour the marinade over it. Seal the bag and refrigerate for at least 1 hour, or up to 8 hours.3. Preheat your grill to medium-high heat. 4. Discard marinade and definitely do not reuse it. 5. Place the duck breast on the preheated grill. Grill for about 5-7 minutes per side or until it is cooked through. 6. Let the duck breast rest for about 5 minutes before slicing or serving.