1. Combine first 5 ingredients in a small bowl; stir well. Place mushroom caps, gills up, in a shallow dish. Pour teriyaki mixture evenly over gills. Cover and chill at least 1 hour.
2. Prepare grill.
3. Place mushroom caps, gills down, on grill rack coated with cooking spray. Grill, covered, 5 minutes on each side or until tender. Cut mushroom caps into 1/2-inch-thick slices. Sprinkle with sesame seeds, if desired.
carbo rating: 5