Preheat oven to 350 degrees. Spray an 8x8-inch baking dish with cooking spray.
In a large mixing bowl, combine oats, brown sugar, baking powder, salt, and cinnamon. Stir with a wire whisk to break up clumps.
3 cups quick oats, 1 cup light brown sugar, 2 teaspoons baking powder, 1 teaspoon salt, 1/2 teaspoon ground cinnamon
In a separate smaller bowl, add the lightly beaten eggs (I crack the eggs into the small bowl and just use a fork to mix), milk, and melted butter. Stir with a whisk.
2 large eggs, lightly beaten, 1 cup milk, 1/2 cup (1 stick) butter, melted
Add the milk mixture to the oatmeal and stir together until everything is combined. Add the fruit and gently mix together. 3/4 cup peeled, chopped apple, 1/2 cup fresh blueberries, 1/2 cup fresh or canned peaches, chopped
Spread the oatmeal batter into the prepared dish. Top with additional chopped peaches and blueberries, if wanted.
Bake for 35-40 minutes. Edges will be golden brown and the middle should look set but still slightly jiggly. Let it cool for about 10-15 minutes and then cut into squares. Serve with a drizzle of milk, or put milk in the bottom of the bowl, and additional chopped fruit to garnish.