Evenly divide the bread slices between two greased 9x13-inch baking dishes. Set aside.
In a large bowl, whisk the milk, eggs, sugar, zest, vanilla and salt. Pour evenly over the bread. Let it soak for five minutes. Turn the bread slices over. Cover and chill for 12 hours (or overnight).
Before serving, preheat the oven to 325° F. In a small bowl, mix the sugar and cinnamon. Sprinkle evenly over bread.
Bake, uncovered, 35 to 45 minutes, until crisp on the outside and tender on the inside. Serve immediately with powdered sugar, fresh fruit, or syrup.