Preheat your oven to 400°F (200°C). For the best results and to prevent sogginess, place a wire cooling rack over a large rimmed baking sheet.
Clean the mushrooms by wiping each cap with a damp paper towel. Do not submerge them in water. Carefully remove the stems by twisting them until they pop out. Set the caps aside and finely chop the stems.
Heat the olive oil in a medium skillet over medium heat. Add the minced beef bacon and cook until it begins to crisp, about 3–4 minutes.
Add the chopped mushroom stems and minced shallots to the skillet. Sauté for 5–6 minutes, or until the moisture from the stems has completely evaporated and they are lightly browned.
Stir in the minced garlic and cook for 30 seconds until fragrant. Remove the skillet from the heat and let the mixture cool slightly.
In a medium mixing bowl, combine the softened cream cheese, Parmesan cheese, fresh parsley, thyme, black pepper, and cayenne pepper. Add the sautéed mushroom stem mixture and stir until well combined.
Fold in the panko breadcrumbs until evenly distributed throughout the filling.
Use a small spoon or a piping bag to fill each mushroom cap generously, pressing the filling down slightly and mounding it over the top.
Arrange the stuffed mushrooms on the prepared wire rack. Bake for 18–22 minutes, or until the mushroom caps are tender and the stuffing is golden brown and bubbling.
Allow the mushrooms to cool for 5 minutes before serving to let the filling set.