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Chop the stems finely -- you'll be using in the stuffing. You should also scoop out a bit of the insides of the mushrooms with a spoon to make room for the stuffing. Place 3 slices of finely-chopped bacon, 1/2 cup of chopped onion, 1 finely-chopped clove of garlic, and the chopped stems together in a frying pan. Sauté them together in 2 tbsp. of olive oil. Cook them until the onion is soft and the stems have softened. This should take about 3-5 minutes.  Stir in 1 cup of shredded mozzarella cheese, 1/2 cup of soft breadcrumbs, 1/4 tsp. of oregano, and 1/4 tsp. of salt into the mixture. Gently mix the ingredients until they are all combined.   Bake them for ten minutes -- long enough for the cheese to melt, but not long enough to burn the ingredients. Enjoy this delicious treat on its own or with a dollop of sour cream.

Summary:
Preheat your oven to 375°F (190°C). Remove the stems from 1 lb. of button mushrooms. Make the stuffing. Drain the olive oil from the mixture. Stir in the remaining ingredients. Place the stuffing in the mushroom caps. Place the mushroom caps on a cookie sheet. Bake them for 10 minutes. Serve.