Heat a large frying pan. Place 2 teaspoons of oil into the pan. When the pan is hot, add the chicken breasts and cook on each side for 4 minutes until cooked. After 8 minutes, remove the pan from the heat. Leave the chicken in the pan and allow it to rest before you use it for the sandwich to ensure it is tender.
Finely chop the chives. Remove the stalk from the parsley and discard. Finely chop the parsley leaves. Cut the lemon in half and juice it.
Place the egg yolks in a bowl, alongside the lemon juice. Whisk the two ingredients together well and whilst whisking, gradually pour the oil into the centre of the bowl until all of the oil is incorporated and mixture has become thicker.
Once all the oil has been added, mix in the salt, pepper and the fresh herbs.
Peel the red onion and cut it in half. Slice the red onion very finely and place into a mixing bowl. Wash the spring onions and peel the outside skin. Thinly slice the spring onions and place it with the red onion. Mix well. Add the mustard, vinegar and sugar into the bowl and mix well.
Add salt and pepper to taste.
Slice the chicken finely and mix it with the mayonnaise. Place a large tablespoon of chicken onto one slice of the buttered bread. Smooth the mixture over. Top the chicken with some of the onion slaw and finish with some fresh rocket.
«When placing the slaw into the sandwich, drain off the excess liquid or the sandwich will become soggy.»