Apple-walnuts stuffed mushrooms

32 lg mushrooms, fresh vegetable cooking spray
3 tbsp celery, finely chopped
1/2 cup apple, minced
2 tbsp fine, dry breadcrumbs
1 tbsp parsley, fresh, chopped
2 tbsp walnuts, finely chopped, toasted
1 tbsp Blue cheese, crumbled
2 tsp lemon juice

1. Clean mushrooms with damp paper towels. Remove stems, finely chop 1/3 cup of stems, reserving remaining stems for another use. Set mushroom caps aside.
2. Coat a small skillet with cooking spray, place over medium high heat until hot. Add 1/3 cup reserved chopped mushroom stems and celery; saute 2 minutes or until tender.
3. Combine celery mix, apple and next 5 ingredients in a small bowl, stir well. Spoon 1 1/2 tsp apple mix into each reserved mushroom cap. Place mushrooms in a 15x10" jelly roll pan, bake at 350 for 15 minutes.