Preheat the oven to 190°C (170° fan) | 375F | gas 5.
Heat the oil in a saute pan set over a medium heat until hot. Add the leek, onion, carrot, and a pinch of salt, sweating for 5 minutes until softened.
Stir through the tomato puree and lemon juice, cooking for a further minute. Pack the vegetable mixture on top of the hake fillets.
Sit the fillets in a roasting dish and season with a little more salt and pepper. Roast in the oven for 8 – 10 minutes until the flesh is cooked through and firm yet slightly springy to the touch.
Remove from the oven and leave to rest briefly before serving with a garnish of bay leaves and lemon slices on the side.