CHICKEN AND MUSHROOM PASTRY PARSELS

510 g chicken breast fillets, sliced thinly
100 g mushrooms, chopped finely
1 small leek, sliced thinly
1/2 cup low-fat sour cream
1 tablespoon Dijon mustard
1/2 cup finely grated low-fat cheddar cheese
2 teaspoons finely chopped fresh tarragon leaves
8 sheets fillo pastry
Cooking-oil spray

Heat oiled large pan; cook chicken, in batches, until lightly browned and cooked through. Place mushrooms in same pan; cook, stirring, until lightly browned and tender. Add leek; cook, stirring, until leek is softened. Return chicken to pan with sour cream, mustard, cheese and tarragon; cook, stirring, until combined. (Can be made ahead to this stage. Cover, refrigerate until required.)