1. Heat the butter in a frying pan, add the onion and fry for 4-5 minutes until softened. Remove from the heat and stir in the breadcrumbs, coriander seeds, grated lemon zest and sweet chilli sauce.
2. Preheat the grill to medium. Press the breadcrumb mixture over the flesh side of the mackerel fillets then grill for 4 minutes until golden and cooked through.
3. Meanwhile, make the salad dressing by whisking together the olive oil and lemon juice in a small bowl.
4. Serve the mackerel fillets garnished with rocket leaves, raspberries and the lemon oil dressing.
Recipe courtesy of Waitrose