Preheat oven to 350°.
. Pierce potatoes with a fork. Microwave at HIGH 12 to 15 minutes or until tender; cool slightly and cut into 1/2-inch slices. Layer potato slices in a 13 x 9-inch baking dish coated with cooking spray.
. Heat oil in a large nonstick skillet over medium heat. Add onion and garlic; sauté 5 minutes or until soft. Spoon onion mixture over potatoes.
. Place flour in a small bowl; gradually add milk, stirring with a whisk until blended. Pour mixture into pan, and cook over medium-high heat 2 minutes or until thick, stirring constantly. Add cheese and next 4 ingredients; stir until cheese melts. Pour cheese mixture over potato mixture.
. Bake at 350° for 35 minutes or until bubbly. Let stand 10 minutes before serving.