Smoked mackerel, pea and spinach frittata

Method

1. Heat the grill to medium-high. Heat a glug of oil in a deep 23cm non-stick frying pan, add the onion and fry over a medium heat for 5 minutes fry until starting to soften. Add the garlic and cook for 1 minute more, then reduce the heat and add the spinach in batches, stirring regularly, until it has fully wilted.
2. Meanwhile, put the eggs in a large jug with the dill, lemon zest and juice and creamed horseradish, then whisk together with salt and pepper. When all the spinach has wilted, add the peas and mackerel, then pour the egg mixture over the fish and veg.
3. Gently mix everything together, then turn the heat to low and cook gently for 6-8 minutes. The base of the frittata should be set and golden. Sprinkle with the cheese and grill for 5-8 minutes until the top has set and the cheese is golden. Garnish with the remaining dill.