Preheat oven to 475F and prepare a 9x13 inch pan by greasing with butter or non-stick spray.
In a large bowl combine oat milk, eggs, maple syrup, vanilla bean paste, cinnamon and pumpkin pie spice. Whisk until ingredients are fully combined and set aside.
Next, cut an entire loaf of brioche bread into 1 inch cubes.
Add the cubed brioche pieces to the greased pan and pour the milk mixture over the bread. Use a spoon to gently mix, you want to ensure each piece is coated in the mixture.
In a small bowl add in the melted butter, flour, coconut sugar and salt. Mix well until a crumble starts to form, then use your hands to crumble the streusel evenly over the french toast bake.
Cover the pan with foil or parchment paper and bake for 3o minutes.
Let cool for 10 minutes, slice into and enjoy!