Cook the bacon strips in a large skillet over medium heat until crispy.
Drain on paper towels.
While the bacon is cooking, remove the stems from the mushrooms. Set the caps aside and chop the stems.
Place the butter in a skillet with bacon grease. When melted, stir in the mushroom stems, onion and garlic, thyme, salt and pepper.
Cook, stirring frequently until the onions are carmelized, approximately 15 minutes.
Preheat the oven to 350º.
Once the onion mixture has reached a deep, rich brown color, place into a blender or food processor along with the bacon,cream cheese, blue cheese and panko crumbs.
Blend on low until ingredients are roughly chopped and evenly combined.
Stuff cheese mixture into the caps and place onto a baking sheet with parchment paper or sprayed with pan coating.
Bake in oven until bubbly and lightly browned (10-15 minutes).