Mussel fritter and rocket mayo sandwiches

Ingredients

• Rocket mayo
• 1 cup good-quality mayonnaise
• 1 cup rocket leaves, roughly chopped
• 1/2 teaspoon finely grated lemon zest
• 1 medium lemon, juice only
• flaky sea salt
• Mussel fritters
• 15 fresh green-lipped mussels
• 1 large free-range egg
• 1/4 cup milk
• 1/2 cup self-raising flour
• 1 medium red onion, finely chopped
• 2 tablespoon vegetable oil
• 8 thick slices fresh wholemeal bread, buttered