Heat an ovenproof casserole or frying pan and add oil. Brown the sausages on each side until golden, about 10 minutes. Remove and place on a paper towel to absorb excess fat. Set aside.
Add onions and garlic and sauté for 5 minutes until translucent. Add ginger and apple and sauté for a further 3 minutes until the apple start to soften. Stir in curry paste, chicken stock and tomatoes and bring to the boil.
Add the browned sausages, bring back to the boil, cover, then place in a preheated oven at 180°C for 20 minutes.
Place cornflour into a small bowl and cover with warm water, stir until smooth. Remove casserole from the oven and stir through the cornflour. Cover and return the casserole to the oven for a further 5 minutes to thicken.
Lastly, sprinkle the casserole with chopped parsley and serve with hot mashed potato or steamed rice.