Preheat the oven to 180°C, fan 160°C, gas 4. Line a cupcake tin with 12 cases.
In a large bowl, place the flour, sugar, carrot, orange zest, half the walnuts, the mixed spice and the baking powder. In a separate bowl, gently beat together the golden syrup, sunflower oil and eggs.
Pour the wet ingredients into the dry and mix well. Spoon into the paper cases and bake for 25 minutes. Cool completely.
Meanwhile, make the icing: whisk together the butter and icing sugar until soft. Stir in the cream cheese and whisk until combined. Spoon into a piping bag with a star-shaped nozzle.
Pipe the icing onto the cooled cupcakes and decorate with the remaining walnuts, the extra carrot strips and the mini carrots and eggs.