Blitz the mushrooms until finely chopped and mix with the chicken mince, egg, breadcrumbs and cumin. Season well and form into patties. Set aside for 15 minutes while you make the sauce.
Finely chop the tarragon leaves and mix with the cream.
Bring the chicken stock to the boil and reduce by half. Add the cream, bring back to the boil and then reduce by half again. Stir in the mustard. Check and adjust the seasoning.
Meanwhile, cook the chicken burgers under the grill or in a sauté pan until cooked through.
Heat the pitta breads until warm and soft then slice open.
Fill each pitta bread with a warm chicken burger, top with a slice of cheese and drizzle with the warm tarragon sauce.
Serve immediately with a little rocket or watercress.
