Preheat oven to 220c/425f/Gas 7.
1 Halve the leek and rinse well. Fill a deep pan one third full with vegetable oil and heat. Cut one leek half into thin strips and deep fry until brown and crisp. Drain on kitchen paper.
2 For the Omelette: Beat the eggs in a bowl, add 55g/2oz grated cheese and the double cream. Heat an omelette pan, pour in the egg mixture and add the chopped chives. Cook gently, stirring to draw the mixture from the edge of the pan to the centre as it cooks. Serve the omelette on a plate.
3 Cook the potato in a pan of boiling water until tender. Cut the remaining leek into thin rings and dice two bacon rashers. Heat 1 tbsp olive oil in a frying pan with the diced bacon and stir in half the leek rings, 1 tbsp chopped parsley, breadcrumbs and 25g/1oz grated cheese.
4 Place one mackerel fillet on a baking sheet skin-side up and spoon the breadcrumb mixture on top. Cook in the oven for about 8-10 minutes, or until cooked through.
5 Heat 1 tbsp olive oil and 15g/ 1/2oz butter in a frying pan. Add the tomato chunks and 1/2 tbsp chopped parsley and cook until the tomato is softened.
6 Drain and mash the potato with the mustard and 15g/ 1/2oz butter. Serve the baked fish with the mash and tomatoes and sprinkle over the deep fried leeks. Remove the skin from the remaining mackerel fillet and sprinkle over the chopped dill and chervil.
7 Use the back of a knife to stretch out the remaining bacon and then wrap the bacon around the fish and secure with a cocktail stick.
8 Heat a griddle pan, add the mackerel and cook for 4-5 minutes on each side, adding the lime and lemon halves and remaining leek rings to the pan halfway through cooking. Serve on a plate.