01 - Preheat oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with nonstick spray or butter.
02 - Distribute the bread cubes evenly across the bottom of the prepared dish.
03 - Combine eggs, almond milk, pumpkin puree, protein powder, maple syrup, vanilla extract, all spices, and salt in a large mixing bowl. Whisk thoroughly until smooth.
04 - Pour the wet mixture over the bread cubes, pressing lightly so all pieces are saturated.
05 - In a small bowl, blend brown sugar and cinnamon. Sprinkle evenly over the casserole. Add nuts, if desired.
06 - Allow the casserole to sit at room temperature for at least 10 minutes, or cover and refrigerate overnight for enhanced texture.
07 - Transfer dish to the oven and bake for 40 minutes, until the center is set and top turns golden brown.
08 - Let cool for 10 minutes after baking. Slice and serve warm, optionally with extra maple syrup or Greek yogurt.