Heat oven to 375. In a shallow bowl, beat egg w/ a little salt, pepper and 1 tsp garlic powder.
In another shallow bowl, mix together bread crumbs, 1 tsp garlic powder and parmesan cheese. In small bowl mix butter w/ lemon juice. Pour about 2/3 butter mix into bottom of a 9" x 13" baking dish. Spread mushrooms evenly into bottom of baking dish.
Dip each chicken breast into egg mix, then coat w/ bread crumb mix. Place chicken on top of mushrooms. Drizzle remaining butter mix over chicken. Sprinkle chicken w/ parsley. Bake about 45 min, or until juices run clear.