Stir together first 8 ingredients; remove and reserve 1 cup honey-Dijon mustard mixture.
Place pork in a large shallow dish or zip-top plastic freezer bag; pour remaining honey-Dijon mustard mixture over pork. Cover or seal, and chill, turning occasionally, 2 hours.
Remove pork from marinade, discarding marinade.
Grill pork, covered with grill lid, over medium-high heat (350° to 400°) 8 to 9 minutes on each side or until a meat thermometer inserted into thickest portion registers 150°. Remove from grill, and let stand 10 minutes. Cut pork into slices.
Bring reserved mustard mixture and 1/4 cup water to a boil in a saucepan; reduce heat, and simmer 2 minutes. Sprinkle peanuts over pork, and serve with sauce. Garnish, if desired.