Preheat the oven to 375ºF. Lightly coat a 2-quart baking pan with cooking spray.
Line a baking sheet with foil and pour the almonds on top. Toast the almonds until lightly golden, 7 to 9 minutes. Reserve ¼ cup sliced almonds and coarsely chop the remaining.
In a large bowl, stir together the oats, chopped almonds, baking powder, cinnamon, ginger, and salt.
In a medium bowl, whisk together the milk, maple syrup, egg, butter, and vanilla. Stir the milk mixture into the oat mixture to combine. Add ¾ of the blueberries and raspberries and stir again.
Transfer the mixture to the prepared baking pan. Sprinkle with the remaining berries and almonds. Bake until the oatmeal is set and golden brown, 55 to 60 minutes.
Let the oatmeal cool for 10 minutes. Scoop a portion into a bowl and serve with additional maple syrup and a spoonful of Greek yogurt.
