Chicken pie with cheesy mash

Ingredients

• 2 teaspoon vegetable oil
• 1 medium_piece (150g) brown onion, chopped finely
• 750 gram minced (ground) chicken
• 1 medium_piece (120g) carrot, chopped finely
• 2 (300g) stalks celery, trimmed, chopped finely
• 1/4 cup (35g) plain (all-purpose) flour
• 1 cup (250ml) chicken stock
• 2 tablespoon worcestershire sauce
• 155 gram button mushrooms, quartered
• 3/4 cup (120g) frozen peas
• 2 x 600g tubs prepared mashed potato
• 1/2 cup (40g) parmesan, finely grated