Heat oven to 400 degrees. In 2-quart saucepan over medium heat cook potatoes, covered, in 2 inches boiling water until almost tender, 6 to 8 minutes; drain. In large nonstick skillet over medium heat, heat oil. Add mushrooms; saute over high heat until tender and liquid has evaporated; set aside.
In small bowl combine flour, salt and pepper. Coat shallow 1 1/2-quart baking dish with vegetable cooking spray and cover bottom with a layer of potatoes; sprinkle with a little of the flour mixture. Add a layer of mushrooms. Sprinkle with some of the cheese; dot with butter. Repeat layers until all ingredients are used, ending with butter; pour milk over.
Bake 30 minutes until potatoes are tender and top is browned. Sprinkle with parsley.
Nutritional Information Per Serving: 320 calories; 16 g fat; 40 mg cholesterol; 490 mg sodium; 35 g carbohydrate; 4 g fiber; 13 g protein.