Bacon Cheddar Mushrooms

3 piece raw bacon slices (cooked, drained, and diced) 

3/4 cup mushrooms
1 tbsp salted butter
1 tbsp fresh chopped onion
3/4 cup Cheese, cheddar, sharp, shredded

Preheat oven to 400P degrees F. Place bacon in a large, deep skillet. Cook over medium-high heat until evenly brown. Drain, dice and set aside.
Remove mushroom stems. Set caps aside. Chop stems into fine dice.
In a large saucepan over medium heat, melt the butter. Slowly cook the diced stems and diced onion, stirring occasionally until the onion is soft. Remove from heat. In a medium bowl, stir together the mushroom stem mixture, diced bacon and 1/2 cup shredded cheddar cheese. Mix well and scoop the mixture into the mushroom caps. Add remaining shredded cheddar to top of each cap. Bake in preheated oven 15 minutes, or until the cheese has melted.