Preheat the oven to 200C/180C Fan/Gas 6. Line a 6 hole muffin tin.
In a large bowl, combine the flour, sugar, cinnamon and baking powder. Make a well, and pour in the egg, butter (make sure it has cooled a little), oil and milk. Stir gently with a wooden spoon until just combined. Add the chocolate chips and just stir once or twice to incorporate.
Make the crumb topping by combining all ingredients in a small bowl - mix until it resembles wet sand, but not so far that it sticks together/forms a paste.
Scoop the muffin batter into the muffin tin. Add over the crumb topping. Bake 15-20 minutes on the middle shelf, until golden. Remove and let cool.
Make the glaze by combining icing sugar and milk. Stir to reach desired consistency (fairly thin). Drizzle over and eat!