Preheat the oven to 375 °F
Spray a 13x9 - inch baking pan with nonstick spray
Whisk together the yogurt, egg, egg whites, sugar, vanilla, baking powder and salt
Stir in the skim milk
Stir in the 3 cups of uncooked oats
Stir in the berries and chocolate chips
Pour the batter in the baking dish, pop it in the oven and bake for about 45 minutes. If you're using frozen berries, you might need to bake it a little longer (up to an hour), so keep your eyes on it! You'll know it's done when a knife or toothpick inserted in the center comes out clean.