Using a soft mushroom brush or a damp cloth, clean mushrooms to rid of any grit or dirt.
Gently break off stems from caps and finely chop.
In a pan over medium-high heat, cook bacon until lightly browned and crisp. Remove from heat and set aside. Remove rendered fat except for about 1 tablespoon.
Add shallots and garlic to the pan and cook until softened.
Add chopped mushroom stems and continue to cook, stirring regularly, for about 2 to 3 minutes or until tender. Season with salt and pepper to taste. Remove from heat and allow to cool.
In a bowl, beat cream cheese until smooth and fluffy.
Add blue cheese, mushroom mixture, crisp bacon, and green onions. Stir to combine.
Arrange mushroom caps gills side down on a baking sheet and lightly brush with olive oil.
Bake in a 400 F oven for about 4 to 5 minutes or just until mushrooms start to leak.
Turn mushroom caps to cavity side up and using a small spoon, fill with stuffing mixture.
Return to oven and bake at 400 F for another 10 minutes or until filling is heated through and tops are golden brown.