Coat a 9 x 5 inch baking dish with nonstick cooking spray and fill with bread cubes. Place eggs, milk, salt, 1/2 tsp cinnamon, nutmeg, 2 tsp sugar and vanilla in a medium bowl and whisk to combine. Pour the egg mixture over the bread, making sure to coat all of the bread pieces. Cover and refrigerate overnight. The following morning remove the french toast from the refrigerator and preheat the oven to 350°F. Melt the butter and drizzle it over the top of the french toast. Sprinkle the top with remaining cinnamon and sugar, followed by the frozen mixed berries. Bake until golden brown and puffy, about 30 - 40 minutes. Let cool 5 - 10 minutes before serving.