REmove stems from mushrooms.
Saute stem pieces and caps in oil until browned and set aside.
Place spinach in bottom and sides of a shallow 10 inch baking dish.
Sprinkle onion, melted butter, salt, garlic salt and seasoned salt on spinach.
Sprinkle 1/2 cup cheddar cheese on spinach.
Place mushrooms on cheese.
Season with garlic salt and sprinkle with remaining 1/2 cup cheese.
Bake, uncovered, at 350*F for 20 minutes.
