Preheat oven to 350°F. In an 8 x 8-inch square cake pan, use a fork to mix together flour, sugar, baking soda, salt and spices.
Create a shallow well in the center of the pan and add water, oil, vanilla extract and vinegar. Mix with a fork until well combined, making sure to reach all the edges. Sprinkle apple over the top, pushing the pieces into the batter.
Bake until a tester inserted in the center comes out clean, about 40-45 minutes. Let cool at least 30 minutes before serving.
For an easy frosting, combine ¼ cup soft butter, 5 tablespoons maple syrup, and 1 ½ cups powdered sugar. Beat until light and fluffy, about 5 minutes.
