Preheat oven to 350 degrees F. Mist a 9x13-inch baking dish with nonstick cooking spray and set aside.
In a medium bowl, whisk together the oats, cinnamon, salt, and baking powder. In a large bowl, gently whisk the eggs. Add the yogurt, sugar, vanilla, and almond milk; whisk well. Pour the wet ingredients into the dry and mix until combined. Fold in the blueberries and walnuts until incorporated.
Spread oat mixture into the prepared baking dish and bake for 45-50 minutes or until golden and set. Refrigerate leftovers for up to 4 days.