Do not clean mushrooms with water, it makes them watery, and they are grown in sterile soil so a speck of dirt won't hurt, use a mushroom brush or a damp paper towel.Clean and destem mushrooms and saute in about 1 T butter till slightly cooked. Remove and set on cookie sheet underneath side up to stuff. In a food processor or blender, chop the green onions, then add and pulse the cooked sausage till crumbled fairly small. Add softened cream cheese and parmesan cheese and blend til thoroughly mixed. Use a teaspoon or piping bag to mound filling onto mushroom caps. Bake at 350 for about 10 minutes. Then set oven to broil and brown tops lightly. Serve hot.