Preheat the oven to 400. Line a 12 cup muffin tin with paper liners or spray with cooking spray.

In a large bowl, whisk together the sugar, flour, baking powder, salt, and cinnamon. In a small bowl or measuring cup, whisk together the oil, egg, milk, and vanilla. Pour the wet ingredients into the dry ingredients and mix until just combined.

Gently fold in the grated apple. Scoop into the prepared muffin tin, filling 3/4 full.

To make the topping, whisk together the sugar, flour, and cinnamon with a fork. Grate in the cold butter, then break it up using a fork or your fingers to form a crumbly mixture.

Sprinkle the streusel liberally over the top of the muffins. Bake 15-20 minutes, or until lightly browned on top.