Overnight Oatmeal Bars with Mixed Berries

Combine oats and milk in a large bowl or measuring cup. Cover and let soak in the refrigerator until much of the milk is absorbed, at least 8 hours and up to 12 hours.

Preheat the oven to 375 degrees F (190 degrees C). Coat an 8-inch square baking pan with cooking spray.

Stir egg, maple syrup, oil, vanilla extract, cinnamon, baking powder, and salt into the soaked oats until well combined. Spread the mixture into the prepared pan. Top with mixed berries.

Bake the oatmeal until it springs back when touched, 25 to 30 minutes. Let cool in the pan for 10 minutes. Cut into twelve 2x2-1/2-inch bars. Loosen and remove with a flexible spatula. Serve warm.