In a large shallow bowl, crack your eggs. Add the oat milk, cinnamon, maple syrup, and vanilla. Whisk very well to break up the yolks and combine them into a homogenous mixture.
Melt the butter in a skillet over medium heat.
Carefully dip each piece of bread into the custard. Saturate both sides of the bread.
Quickly remove the bread and add it to the hot skillet. Repeat with the rest of the bread slices. You will likely have to cook these in a few batches, with 2-4 pieces of French toast in each batch.
Cook on the first side for 2-3 minutes. Once browned, flip the toast and cook for another 2 minutes. Once both sides are golden brown, remove them to a plate.
Once all the French toast is cooked, top with banana slices, maple syrup, and butter. Serve warm.