Preheat oven to 350°F (177°C). Grease an 8-inch square baking dish with butter.
In a large bowl, combine the diced apples, flour, oatmeal, brown sugar, baking powder, baking soda and cinnamon. Cut the butter into small pieces and add to the mixture, stirring until the butter is evenly distributed.
Add the warm water to the mixture and stir until just combined. Do not overmix.
Pour the mixture into the greased baking dish and spread evenly.
Bake for 30-35 minutes, or until the top is golden brown.
Remove from oven and let cool before serving.
Interesting Facts
Apple squares can be served warm or cold.
You can also add walnuts or other nuts to the recipe for a crunchy texture.
You can serve apple squares with a dollop of whipped cream or a scoop of ice cream for an extra special treat.