Slice the aubergine then put all slices in a single layer on the baking sheet and brush lightly with some olive oil, sprinkle with salt & pepper. Bake in the oven for about 20 minutes or until lightly brown.
Steam or boil the potatoes for 15-20 minutes but do not over cook them, leave them to cool then cut into thick slices.
Heat 1 tbsp olive oil in a pan over a medium heat. Add the onion & garlic and sauté for about 4-5 minutes. Add the leek and courgette and sweat off for a further 1-2 minutes.
Add the soya mince and lentils, mix well then add herbs and spices.
Add the tomato purée, chopped tomatoes, and salt & pepper to taste. Finally, add enough stock to just cover the vegetables and let simmer on low heat for about 10-15 minutes.
For the béchamel sauce, add the plant-based milk to a pan.
Mix in the cornstarch, nutritional yeast, salt and pepper, and whisk. Add the vegan butter and bring the mixture to a boil.
Let simmer on low heat for a few minutes until it thickens. Whisk continuously. Remove from heat.
Grease a 13"x9" (33x23 cm) or larger baking dish.
Put a layer of the lentil mix, then a layer of the roasted aubergine, add another layer of the lentil mix then top with a layer of the sliced potatoes.
Finally pour the béchamel sauce on top and spread evenly. Add vegan cheese to taste (optional).
Bake in the oven for about 30 minutes or until golden brown