Preheat the oven to 180C and line a 12 hole muffin tin. Place the margarine/butter in a small, heat proof bowl and microwave in 20 second increments until it's fully melted. Leave to one side.
Place the flour, sugar, baking powder, bicarbonate of soda, salt and spices into a large bowl and mix together with a wooden spoon.
Add in the eggs, cooled, melted margarine, pumpkin puree and black treacle and mix until the mixture forms a sticky, smooth batter. This will be a thick batter, but don't be tempted to beat it. Just mix until everything is combined and there are no lumps of flour.
Divide the mixture between your muffin liners. I used a cookie scoop and placed 2.5tbsp of batter into each liner. You want to fill the liners about 3/4 of the way.
Place in the oven for 18-22 minutes, until risen and an inserted skewer into the centre comes out clean. Leave to cool in the pan, before transferring to a wire rack with kitchen paper underneath.
For the glaze: Sift the icing sugar into a small bowl, add the ginger and 1/2tbsp of milk. Start bringing the mixture together and then add the remaining 1/2tbsp of milk. Mix until you have a smooth paste which will ribbon off of a spoon, but not so runny it vanishes! This ratio of icing sugar to milk was perfect for this glaze. The glaze should stick to the spoon, but then drizzle easily.
Drizzle the glaze all over the muffins and leave for 10 minutes to set. Of course, you can omit the glaze if you'd rather.
Pumpkin Gingerbread Muffins will keep in an airtight container, at room temperature, for 5 days.