Coat inside of a 3QT crock-pot with non-stick spray. Arrange chicken in single layer in the bottom. Top with mushrooms then sprinkle salt, pepper and garlic powder on top.
Stir together cream cheese, butter, parmesan and milk in a medium saucepan over medium heat-whisking constantly till smooth and heated.
Pour over mushrooms-cook 4-5 h. on low, 2-21/2 on high.
Cook fettuccini in salted boiling water to package directions, drain well and add to alfredo sauce. Garnish with Parmesan cheese.