Spiced parsnip shepherds pies

Name: Spiced parsnip shepherd's pies
Ingredients: 2 tbsp sunflower oil; 1 large onion, chopped; 2 garlic cloves, crushed; small knob of ginger, peeled and granted; 2 tbsp medium curry powder; 500g minced beef or lamb; 400g can chopped tomato; 100g frozen pea; 600g parsnip, peeled and chopped into large chunks; large potato, peeled and chopped into large chunks; 1 green chilli, deseeded and chopped; large bunch coriander, chopped; 2 tsp turmeric; juice of 1 lemon; 50g butter