Place a 30cm non-stick frying pan on a medium-high heat.
Place all the mushrooms in the dry pan, tearing up any larger ones.
Let them toast and get dark golden and nutty, tossing occasionally, while you peel and finely slice the red onion and slice the chicken breasts into 1cm-thick strips.
When the mushrooms look good, add the onion and chicken to the pan with 1 tablespoon of olive oil.
Cook for 5 minutes, tossing often, then add the mustard, cream and 150ml of water.
Bring to the boil, then simmer until you’ve just got a loose saucy consistency and the chicken is cooked through.
Taste, season to perfection with sea salt and black pepper, and dish up.
