Baked Oatmeal for a Crowd With Berries and Seeds

Ingredients: 4 cups rolled oats 1/2 cup brown sugar or maple syrup 2 teaspoons baking powder 2 teaspoons ground cinnamon 1/2 teaspoon salt 2 cups milk (or a milk alternative) 1/2 cup melted coconut oil or butter 4 large eggs 2 teaspoons vanilla extract 2 cups mixed fresh berries (such as blueberries, raspberries, and strawberries)