Preheat the oven to 180ºC, brush a 2 litre (8-cup) capacity bundt pan with melted butter to lightly grease, dust with flour and shake off any excess.
Use the grater attachment on your food processor to finely grate the carrot and zucchini, place the carrot-zucchini mixture in a clean tea towl and squeeze out all excess moisture, then transfer to a large bowl.
Place the walnuts in the clean bowl of the food processor and process until finely chopped. Add to the carrot mixture.
Place the egg, sugar,oil and orange rind and juice in the bowl of the food processor and process until light and frothy. Sift over the flour and cinnamon and process until just combined. Add to the carrot mixture and use a large metal spoon to gently fold until just combined. Spoon into the prepared pan and smooth the surface.
Bake in the preheated oven for 50-55 minutes or until a skewer inserted into the centre comes out clean. Set aside for 10 minutes to cool slightly before turning onto a wire rack.
Fudge Icing: Meanwhile, to make the fudge icing, place the sugar, butter and cream in a medium saucepan over a medium-low heat. Cook, stirring, for 3 minutes or until the butter melts. Increase the heat to medium-high and bring to a simmer. Cook, stirring occasionally, for 3-5 minutes or until the fudge thickens slightly. Remove from the heat, add the vanilla and stir to combine. Set aside for 15 minutes to cool slightly.
To Serve: Transfer the cake to a serving plate and drizzle with fudge icing.