Preheat oven to 180°C. Line a 12-hole, 1/3 cup-capacity muffin pan with paper cases. Squeeze excess moisture from zucchini and carrot. Drain on paper towel.
Using an electric mixer, beat oil and sugar in a large bowl for 5 minutes or until mixture is pale. Add eggs, one at a time, beating well after each addition. Stir through zucchini and carrot.
Combine flour, bicarbonate of soda and mixed spice in a bowl. Sift over egg mixture. Add pecans. Stir well to combine. Divide mixture among paper cases. Bake for 30 minutes or until golden and a skewer inserted into the centre of one cake comes out clean. Stand for 5 minutes. Remove cakes to a wire rack. Allow to cool completely.
Make cream cheese frosting: Using an electric mixer, beat butter, cream cheese and orange rind until smooth. Gradually add icing sugar, beating until well combined.
Spread icing over cakes. Serve.
