500 g (1 lb) boneless, skinless chicken breasts, roughly chopped
1 tablespoon wholegrain mustard
3 tablespoons chopped tarragon
1/2 small red chilli, finely chopped (optional)
4 wholemeal buns
béarnaise sauce from a jar
rocket leaves tossed in lemon juice
Place the chicken in a food processor and whizz until smooth. Transfer to a bowl, add the mustard, tarragon and chilli and season well with pepper. Mix together until well blended, then shape into 4 patties.
Lay the chicken burgers on a grill rack lined with foil and cook under a preheated high grill for 4–5 minutes on each side until browned and cooked through. Split the buns and place, cut-side up, under the grill for the final 1 minute of cooking time.
Place a hot burger on the top of each warm bun base and top with a spoonful of béarnaise sauce and a handful of lemon juice-dressed rocket. Cover with the warm bun tops and serve immediately.