In a blender, place the banana, eggs, vanilla, cinnamon, and milk. Blend to combine into a smooth mixture. Mashing the bananas in a bowl will not work.
Pour mixture into a large 9x13 baking dish. Tip: soak as many bread slices as you can fit in your pan at one time, for 2 minutes on the first side, flip, and an additional 1 to 2 minutes on the second side.
Cook:
Heat a large non-stick pan or griddle over medium heat. Once hot, grease with oil or butter. Place the soaked bread slices on the pan and cook for 2 to 3 minutes, without moving the bread, until the bottom is golden and flips easily.
Flip the banana french toast slices and cook the second side for 2 more minutes, until the middles are puffy and the liquid mixture has been absorbed and cooked through. Remove onto a plate and keep warm while you cook the remaining bread slices.
Serve:
Serve warm topped with banana slices, syrup, and any toppings that make your heart happy. Peanut butter over these makes mine skip a beat.