Heat oven to 350°F. Spray 11x7-inch or 12x8-inch glass baking dish with cooking spray. Place potatoes, bell peppers and green onions in baking dish; mix lightly. Top with Alfredo sauce; sprinkle with cheese.
Bake uncovered 40 to 45 minutes or until golden brown. Sprinkle with additional green onion tops and chopped roasted red bell peppers if desired just before serving.