Preheat oven to 375 degrees F.
Clean mushrooms with a damp paper towel. Line a baking sheet with foil and spray with non-stick cooking spray. Place mushrooms topside down on foil lined baking sheet and cook for 5 minutes. Remove from oven and set aside.
Brown ground beef in a non-stick skillet. Season beef with seasoning salt halfway through the cooking process. Once beef is cooked, drain off the fat and place ground beef in a medium bowl to cool. Once beef is room temperature, stir in onions, bacon bits, 2 tbsp. cheese and mayonnaise.
Generously fill each mushroom with the beef mixture. Sprinkle filled mushrooms with grated cheese. Bake for 20 minutes or until the cheese is melted and lightly browned.
by The Savvy Kitchen