Combine the mustard powder, salt, and ground black pepper in a bowl. Mix well and set aside.
Microwave the honey for 15 to 20 seconds and then mix with balsamic vinegar. Stir to mix.
Rub the salt, pepper, and mustard mixture all over each mahi mahi fillet.
Brush the top with the honey and balsamic vinegar mixture.
Heat the grill and then grill each side of the fish in medium heat for 5 to 6 minutes while basting with the honey mixture.
Transfer to a serving plate.
Serve with brown rice and steamed asparagus.
Share and enjoy!