Prepare the mushrooms by cleaning them and removing the stems. Set the mushroom caps aside and finely chop the stems.
Cook the sausage in a large skillet over medium heat. Break it up as it cooks until it’s browned and fully cooked through. Remove the sausage from the skillet and set it aside.
In the same skillet, add a bit of olive oil and sauté the onion, garlic, chopped mushroom stems, and red bell pepper. Cook until the vegetables are soft, about 5-7 minutes.
Return the sausage to the skillet and mix it with the cooked vegetables. Add the almond flour, parsley, oregano, salt, and pepper. Stir until everything is well combined.
Stuff each mushroom cap with the sausage mixture, pressing it in firmly.
Place the stuffed mushrooms on a baking sheet lined with parchment paper.
Bake for 20-25 minutes, or until the mushrooms are tender and the tops are golden brown.
Garnish with extra parsley if desired and serve hot.