Preheat the oven to 200°C fan/220°C/425°F/gas 7.

Place the sliced aubergines on a large lipped baking sheet, sprinkle with salt, and leave for 10 minutes.

Using sturdy paper towels, gently squeeze out the excess moisture from the aubergine slices. Wipe out any excess salt and moisture on the baking sheet and place the aubergines back on the baking sheet. Drizzle with 3 tablespoons of the olive oil. Toss with your hands until well coated, then arrange in one layer.

Bake in the oven for 20–25 minutes, or until softened and lightly browned. Remove from the oven and set aside.

Meanwhile, place the lentils in a medium saucepan and cover with plenty of hot water. Add a pinch of salt, partially cover, and cook for 25 minutes, stirring occasionally, over a medium-low heat. Drain and set aside.

Heat the remaining 2 tablespoons of olive oil in a large pan over medium heat, add the onions, and sauté for 8 minutes, stirring regularly. Add the peppers and sauté for 4 minutes, then stir in the garlic, aubergines, and lentils.

Add the chopped tomatoes and measured water (pour the water into the tomato tin to use up any leftover bits), add the dried mint, and season with salt and pepper. Bring to a gentle simmer and cook for 10 minutes, stirring occasionally. Remove from the heat and set aside.

To make the cheese sauce, melt the butter in a large pan over medium heat. Add the flour and whisk to combine. Pour in the warm milk and whisk constantly until the sauce is thickened, about 6–7 minutes. Add two-thirds of the grated cheese and mix well. Season with pepper and salt (if needed). Remove from the heat.

Preheat the oven to 180°C fan/200°C/400°F/gas 6.

Spread about a third of the filling over the base of a deep 15 x 27 cm (6 x 11 in) baking dish.

Cover with a single layer of dried lasagne (about 3½ sheets should do it). Spoon over another third of the filling and add a second layer of lasagne. Pour over half of the cheese sauce and spread roughly, then top with the remaining filling, spreading gently. Add the last layer of lasagne sheets (4 sheets for good coverage) and spread the rest of the cheese sauce over. Sprinkle the remaining grated cheese over the top.

Bake for 35–40 minutes until the topping is golden brown and bubbling.

Set aside for 10 minutes for the lasagne to settle, then slice to serve.