Crack eggs into a large bowl, preferably with a flat bottom (this will allow for easier dipping). Add the milk, vanilla, and cinnamon. Whisk with fork to combine.
Heat medium skillet over medium heat. When warm, coat lightly with cooking spray.
Dip a piece of bread into the liquid mixture. Turn over and make sure both sides are coated.
Place into the pan and cook each side until lightly browned, and then set aside. Repeat with the other three pieces.
Slice each piece of toast diagonally and arrange onto two places. Zest half of the lemon over one plate, and half over the other plate. Add 5 blackberries to each plate. Sift powdered sugar over the French toast, then add warm syrup as desired.