Super healthy cottage pie

Ingredients

• oil spray
• 600g sweet potato peeled
• 500g lean turkey mince
• 1 large onion finely sliced
• 2 celery sticks finely sliced
• 2 large garlic cloves minced
• 1 cup frozen peas
• 1 tbsp tomato paste
• 1 tbsp Worcestershire sauce
• 1 tsp ground sage
• 1 cup stock (250ml)
• ¼ cup skim milk warmed (60ml)
• 2 tsp light margarine
• 1 spring onion finely chopped