Preheat the oven to 375°F. Spritz a standard size baking sheet with cooking spray. Hollow the mushroom caps removing the stem.
In a medium skillet, cook the bacon then set aside on paper towels to drain. Reserve 3 tablespoon drippings. Add the diced onion and ground beef to the drippings. Season with salt and black pepper. Add Worcestershire sauce. (Adjust salt according to BBQ seasoning used)
Cook until no pink remains, then add minced garlic. Continue to cook until the garlic is fragrant around 1-2 minutes. Drain any excess fat from the pan.
Add cream cheese, barbecue sauce, dill pickles, barbecue seasoning and mustard. Cook until cream cheese has melted and ingredients are evenly distributed.
Remove from the heat. Add 1 cup shredded cheddar cheese. Mix well. Divide filling among mushroom caps, top with remaining cheese.
Bake for 16-18 minutes until the cheese has melted and the mushrooms have softened. Serve immediately.
1) I recommend using a thick barbecue sauce in the filling for the best results. 2) Depending on the size of the mushrooms, the yield may be greater. Extra filling, can be frozen if needed. 3) The mushrooms will release liquid while baking. Drain on a paper towel before transferring to a serving platter