Preheat the oven to 200°C.
Boil the potatoes until soft and mash.
Fry the spring onions in a pan until soft.
Mix the parsley, lemon juice, lemon zest and salmon with the mashed potato.
Divide the mixture into small round fishcake.
Bake for 20-25 minutes until crisp and golden.
Place the watercress and mayonnaise in a blender and blend until smooth.