Preheat oven to 180C. Line muffin tray with 12 cupcake cases. Rinse grated courgette in cold water, then dry well with kitchen paper; set aside.
Using electric whisk, beat eggs, sugar and salt in large bowl for 3mins until pale and thick. Fold in all remaining cupcake ingredients (bar courgette) until well combined, then fold in courgette. Divide mixture between cupcake cases. Bake for 20mins until cooked through, then cool on wire rack.
For icing, melt white chocolate in bowl over pan of boiling water; stir in honey. In another bowl, mix icing sugar with 5tsp boiling water until smooth, then stir in melted chocolate with wooden spoon. Leave to cool.
Place heaped tsp of icing onto each cupcake, smoothing top with back of spoon. Cool for 10mins before sprinkling over grated chocolate.