Thinly slice the fennel and apple and place in a bowl with 2 tbsp of the lemon juice from the dressing, toss until coated in juice.

Mix in the red onion and mackerel.

Divide the salad leaves between two plastic containers with lids, then heap the fennel and mackerel mixture in the centre of the leaves.

Mix all the dressing ingredients together and spoon into a small container.

Refrigerate the salad and dressing until ready to serve.

To serve, drizzle the salad dressing over the salad and toss lightly to mix.