Preheat oven to 375 F. Remove stems from mushrooms; reserve. Season mushroom caps with salt; set aside. Mince stems to yield 1/2 cup; discard remaining stems.
Combine ground beef, minced stems, blue cheese, breadcrumbs, green onions and steak seasoning. Spoon beef mixture evenly into mushrooms.
Place stuffed mushrooms on rack in broiler pan. Bake 15-20 minutes. Sprinkle with chives, if desired.