Recipe method
1. Put the chicken fillets in a large pan and cover with the stock (or water, if you prefer). Bring to a simmer and poach for 8 mins. Take the pan off the heat and set aside to cool.
2. Meanwhile, bring a large pan of water to the boil. Add the potatoes and cook for 8 mins until tender. Drain.
3. Whisk the olive oil, vinegar and mustard in a large bowl. Add the potatoes and mix.
4. Remove the chicken from its liquid, slice it, then mix together with the potatoes.
5. Stir in the spring onions, herbs and lettuce wedges. Season with black pepper.