Preheat the oven to 375
Prepare the flax seed meal mixture by mixing the flax seed meal with the hot water. Set aside until a thick gel forms.
Whisk the flax seed meal mixture with the oat milk, sugar, vanilla, and cinnamon.
Grease a 9x11 ceramic casserole dish. Dip a slice of bread into the custard mixture and place it into the casserole dish. Repeat until you've filled the dish with one layer of soaked bread. Option to layer the bread with banana slices. Drizzle with 2 tablespoon of melted vegan butter. Then, add another layer of the soaked bread. Once you have 2 layers of bread, drizzle the top layer with 2 more tablespoons of melted vegan butter and then pour the remaining custard over the top of the casserole.
Bake in the oven for 30 minutes. Option to broil for the final minute to brown the top more. While the vegan french toast casserole is baking, you may prepare your toppings. I like to add berries, sliced bananas, and maple butter. Prepare the maple butter by mixing 2 tablespoon of melted vegan butter with 4 tablespoon of maple syrup. You may also just use regular maple syrup as a topping.
Use a spatula to scoop out a stack of the french toast and serve warm.