1. Preheat broiler.
2. Remove brown gills from undersides of mushrooms using a spoon; discard gills.
3. Combine milk and flour, stirring with a whisk until blended.
4. Place a large nonstick skillet coated with cooking spray over medium-high heat until hot. Add carrot and next 3 ingredients; sauté 5 minutes. Add spinach; sauté 4 minutes or until spinach wilts.
5. Stir in flour mixture; bring to a boil. Reduce heat; simmer 1 to 2 minutes or until thick. Stir in cooked barley, 1/2 cup cheese, pepper, and nutmeg; cook 1 minute or until cheese melts.
6. Coat reserved mushroom caps with cooking spray; place on a broiler pan. Broil 5 minutes or until tender. Fill each cap with about 1/2 cup spinach-barley mixture, pressing firmly to pack. Broil 3 1/2 minutes.
7. Combine breadcrumbs and 1/2 cup cheese; sprinkle evenly on top of each mushroom. Broil 1 1/2 minutes or until cheese melts.
carbo rating: 19