Grate it. Leave the skin on:
Put it in a small saucepan with a few tablespoons of water, just enough to pool about 1/4 inch at the bottom of the pan. Cover it. Bring it to a simmer using a low heat setting:
It will look like this after about 5 minutes. Stir a few times as it heats. If you use more water or cook longer it will be more like applesauce than grated apple. I stop cooking here because I like the texture.
Let it sit in the pan covered for a couple minutes to even out in temperature. Then add spices. I added about 1/8 teaspoon cinnamon and two shakes of salt. (Salt at the subthreshold level enhances sweet taste without having to add sweetener.)
Side view. I like adding hot spiced apple to a bowl of oatmeal.