Whisk together eggs, milk, vanilla, nutmeg and cinnamon. Place bread in a single layer in a buttered 9 X 13 inch baking dish. Pour egg mixture over bread. Cover and refrigerate overnight.
Mix all topping ingredients.
The next day, preheat oven to 350 degrees. Uncover French toast and carefully spread topping over bread. Bake for 45 minutes. Sprinkle powdered sugar over each serving. Garnish with orange slices.