Preheat your grill to a moderate temperature of approximately 375°F.
For Stuffing:
Using a damp paper towel, clean each mushroom carefully, and remove the stems.
In a mixing bowl, combine cream cheese, shredded cheddar cheese, bacon bits, salt, black pepper, and garlic powder until well combined.
Fill each mushroom cap carefully with the cheese mixture, avoiding overfilling.
Top the filled mushrooms with an additional sprinkle of cheddar cheese and bacon bits.
For Grilling:
Place the stuffed mushrooms on the grill, ensuring they are not over direct heat. Grill for 15-20 minutes, or until the cheese becomes melted and filling is heated through.