In large fry pan with cooking oil - place sliced onion and garlic and cook until translucent - remove. Discard garlic and save onion.
Beat egg with water and parmesan cheese - pound chicken breasts to tenderize - (salt breasts) - Dip breasts in egg mixture and flour and then brown in oil used to fry onion & garlic. Set aside.
In fresh fry pan with fresh oil place onion and mushrooms and cook until mushrooms are heated through. Add 1/3 cup of Marsala Cooking Wine and 2/3 cup of water and simmer until heated through. Add browned chicken breasts and some chopped parsley.
You can then simmer the chicken breasts on the stove (covered) for approximately one half hour - turning once and adding water as needed until cooked through and tender.
When I have a large quantity I put the chicken breasts in a rectangular oven pan and then add the onion-mushroom-Marsala mixture over the top, cover with aluminum foil and place in oven at 375 degrees for approximately one hour - turning them over half way through. Adding water, if necessary.