Pre-heat oven to 190°C
Line a 20cm round shallow tin with baking paper and grease.
Sieve flour, baking powder and allspice into a bowl.
Add the butternut squash, Muscovado sugar, butter, eggs, sultanas, crystallised ginger, orange juice and zest then whisk (by hand) together until blended.
Pour into the tin and level.
Bake in the centre of oven for 20 - 25 mins until a skewer inserted comes out clean.
Allow to cool for 10 mins in tine before transferring to a cooling rack.
Beat together the icing sugar, cream cheese and orange juice to form the frosting.
Spread over the cake when cool and decorate with orange zest strands.