Cut the French bread loaf into 1-inch cubes. Set aside.
In a large mixing bowl, beat the eggs and egg whites together. Then, beat in the milk, lemon zest, and vanilla extract.
Add the bread cubes to the custard mixture and toss to coat. Add the blueberry and stir in gently so you don't burst the berries.
Grease a 9-inch x 13-inch baking dish with non-stick cooking spray. Pour the bread cubes and berries into the prepared dish, then pour any remaining egg mixture over the top.
In a small bowl, combine the brown sugar, flour, butter, and cinnamon until it's crumbly. Sprinkle the streusel evenly all over the french toast.
Cover the dish with foil and refrigerate overnight or at least 8 hours.
Preheat the oven to 350 degrees F. Remove the foil from the dish and bake the french toast for 45 minutes until golden on top.
Remove from the oven and let rest for 5 minutes before cutting into 8 portions and serving warm.