Prepare the Oven and Dish: Spray an 8×8-inch baking dish with oil and preheat the oven to 375°F.
Make the Custard: In a medium bowl, whisk together the eggs, oat milk, salt, cinnamon, maple syrup, and vanilla extract until combined.
Coat the Bread: Dip each halved slice of bread into the egg mixture, making sure it is coated, then arrange the pieces in the prepared baking dish.
Add the Blueberries: Stir the wild blueberries into the remaining egg mixture, then pour the blueberry mixture evenly over the bread in the baking dish.
Bake the French Toast: Bake at 375°F for about 30 minutes, or until the liquid has been absorbed and the bake is set.
Serve: Enjoy the blueberry French toast bake warm.