Lightly brush olive oil on both sides of the potobello mushroom caps then sprinkle the inside lightly with salt (this is optional but I most always do!).
In a skillet brown the sausage meat with green onions crumbling into very small pieces until browned; drain any fat then cool.
In a medium bowl beat eggs with milk, fresh parsley, basil, fresh garlic, cayenne pepper or hot sauce until well combined.
Add in the Parmesan cheese and the ground croutons starting with about 1-1/2 cups ground croutons, you might have to add in more later; mix with a wooden spoon until combined.
Add in the cooked sausage/onion mixture; mix well (the mixture should be wet but still firm enough to hold together if the mixture is too soft add in a small amount more of the croutons at a time just until the mixture binds together).
Season mixture with black pepper to taste.
Spoon the sausage mixture evenly between the portobella mushroom tops.
Place on a lightly greased baking sheet.
Bake in a 350 degree oven for about 15-20 minutes.