Heat oil in a large nonstick skillet over medium heat. Add mushrooms and onion; saute 3 minutes or until tender. Set aside. Arrange 3-1/2 bread slices in the bottom of a shallow 2-1/2 quart casserole coated with cooking spray. Peel, devein, and coarsely chop raw shrimp. Top bread with half of mushroom mixture and half of shrimp. Arrange remaining 3-1/2 bread slices over shrimp; top with remaining mushroom mixture and shrimp. Top with cheese. Combine milk and remaining ingredients in a bowl; stir well, and pour over casserole. Cover and chill at least 8 hours or up to 24 hours. Bake, uncovered, at 350 deg for 55 minutes or until a knife inserted near the center comes out clean. Yield: 8 servings. Per serving: 259 Calories; 9g Fat (33% calories from fat); 22g Protein; 21g Carbohydrate; 98mg Cholesterol; 348mg Sodium Recipe by: Cooking Light, Mar/Apr 1993, page 78 Posted to MC-Recipe Digest V1 #430 by igor@digex.net on Jan 28, 1997.