Whisk together the pumpkin puree, milk, eggs and egg whites, protein powder, and pumpkin pie spice.
Heat a large skillet over medium heat. Add a tablespoon of butter.
When the butter is melted, dip two slices of bread in the egg mixture, soaking the bread fully and letting the excess drip off. Place the slices in the hot pan.
Let cook for about 3 minutes per side, until golden brown and slightly crisp on both sides. Remove from the pan and repeat with the remaining bread and egg mixture, adding another tablespoon or so of butter as needed to fry the french toast.