Preheat the oven to 475°F and grease a 9x13-inch pan with butter or non-stick spray.
In a large bowl, whisk together oat milk, eggs, maple syrup, vanilla bean paste, cinnamon, and pumpkin pie spice. Set aside.
Cut the pumpkin brioche bread into 1-inch cubes and place them in the greased pan.
Pour the milk mixture over the bread cubes, ensuring each piece is coated. Use a spoon to gently mix.
In a small bowl, combine melted butter, flour, coconut sugar, and salt to make the streusel topping. Crumble it evenly over the French toast bake.
Cover the pan with foil or parchment paper and bake for 30 minutes.
Allow it to cool for 10 minutes, then slice and enjoy!