Pound chicken breast pieces into 1/4 inch thick slices. Cut each half breast into 2 to 3 pieces. Combine next three ingredients and mix well. Dredge chicken pieces in flour mixture until well coated.
Spray an 8 x 11 inch baking dish with non-stick cooking spray and set aside. Spray a non-stick frying generously with non-stick cooking spray and place on medium high heat. Fry chicken until underside is browned, then spray uncooked side of chicken with cooking spray and turn, and brown remaining side. Remove from pan and place into baking dish. Cook remaining chicken. As pieces are finished cooking, layer into baking dish.
When finished cooking chicken immediately place mushrooms into the same frying pan. Do not reduce heat. Allow mushrooms to brown. When they have begun to release their water, add garlic and sauté until most of the liquid has cooked away. Remove from heat. Spread mushrooms evenly on top of chicken. Set aside.
Preheat oven to 375 degrees. Place bouillon cubes and water into microwave proof bowl. Place in microwave and heat to dissolve bouillon. Add sherry and sour cream, whisk until smooth. Pour mixture over chicken and mushrooms. Cover with foil. Bake for 25 minutes. Uncover and bake for additional 20 minutes. Serves 6.