Heat a skillet over medium heat and add Italian sausage to cook, breaking it up into small pieces. Add in the garlic and bell pepper and cook, stirring occasionally, until the sausage is browned and cooked through (about 8-10 minutes).
While the sausage is cooking, prepare mushrooms for stuffing by removing the stems and scraping out the ribs. Placing them cap side down on a baking sheet.
Once the sausage has cooked, remove it from heat and let it cool off for a few minutes. Add in the parmesan cheese and mix.
Preheat oven to 400° Fahrenheit.
Scoop some of the sausage mixture into each mushroom to fill them up. Place in the oven to bake for 7-10 minutes.
Allow to cool for a couple of minutes and serve.
Nutrition details are per serving and an estimate provided for those following a Ketogenic or low-carb diet. See our full nutrition information disclosure here. The serving size for this recipe is approximately 4 mushrooms.