Preheat your oven to 350°F and line an 8x8-inch baking pan with parchment paper.
Mix all dry ingredients in a large bowl: oats, brown sugar, baking powder, cinnamon, and salt.
In another bowl, whisk together eggs, milk, applesauce, maple syrup, and vanilla.
Combine wet and dry ingredients, stirring until well incorporated. Fold in your chosen mix-ins.
Pour into prepared pan and spread evenly.
Bake for 30-35 minutes until golden brown and set in the middle.
Let cool completely before cutting into squares.