Place the mushrooms on a baking sheet with the “cup” side facing down, and bake for 10 minutes or just enough to allow some of the moisture to release from the mushrooms.Do this before or while you prepare the filling mixture.
In a large skillet over medium heat, melt the coconut oil or heat the olive oil, and
place the bell peppers and onion in the pan, sautéing until the onions are clear and soft. Add the sausage to the pan, and cook until no pink meat remains (about 5 minutes), stirring occasionally to break up any large chunks of meat.
Add the spinach and garlic, and combine to wilt spinach. Spoon the mixture into each of the mushroom caps, and place them back onto the baking sheet.
Bake for approximately 20 minutes, or until golden brown on top.