Heat 2 tbsp of the oil in a large frying pan over a medium heat. Fry the aubergines for 10-15 mins until golden and softened. Remove with a slotted spoon and set aside.

Fry the onions with the remaining oil for 7-10 mins or until softened. Add the garlic, 1 tbsp of the harissa and the coriander and cook for 1 min more. Return the aubergines to the pan with the tomatoes, lentils, olives and a can of water. Bring to a simmer and cook for 10 mins. Season, then stir through the parsley.

Cook the sweet potatoes in a large pan of boiling lightly salted water for 15 mins. Drain and leave to steam-dry, then mash and stir through the remaining harissa. Spoon the aubergine filling into a large baking dish, scatter over half the feta and spoon over the potatoes. Scatter the remaining feta over the pie.

Heat the grill to its highest setting. Grill the pie for 7-10 mins or until the top is crisp and golden. To freeze, leave to cool completely before portioning out into small freezerproof containers.