Soak the lentils for 15 minutes in warm water.
Preheat the oven to 400º F (200ºC).
Lay the eggplant and sweet potato slices on an oiled pan.
Sprinkle lightly with sea salt and roast in the oven for 10 minutes.
Make the lentil stew by heating the oil in a saucepan.
Add the chopped onion, leek, celery, fennel, garlic. Sautee for 5 minutes and add the lentils and 30 fl oz of water.
Add the tomato puree, nutritional yeast, and spices.
Stir until the lentils are soft, but don’t let them lose their shape. It should take about 15 minutes. The stew should be on the drier side but still creamy.
Line up your eggplant and sweet potatoes and along with your lentils.
Oil a pan where you are going to assemble the casserole.
Start making the bechamel by melting the margarine on a saucepan and adding the flour.
When it starts to brown, cook it for 1 minute more and add the vegetable milk.
Stir with a whisk until it starts to get creamy. Add the nutmeg, salt, and pepper. This sauce gets sticky very quickly, so; you should make it just when everything is ready to assemble. It all should take no more than 20 minutes.
Reduce the oven temperature to 350ºF (175ºC).
Start assembling the dish by arranging the eggplant and sweet potato slices in the bottom of a medium baking pan.
Continue by laying a layer of lentil stew, followed by a layer of bechamel sauce.
Add another layer of sweet potatoes, then eggplants, lentils, and finish with bechamel sauce.
Optionally top with grated vegan parmesan or regular one for a vegetarian version.
Bake for 35-40 minutes. Test to see if the sweet potatoes are tender by inserting a sharp knife down through the center. Remove from the oven and leave to cool for 30 minutes before serving.