For the vegetables:

1. For the eggplants. Preheat oven to 400°F (200°C). Prepare two parchment paper-covered baking sheets. Arrange the eggplant slices on the baking sheets in a single layer, season with sea salt and set aside for 5 minutes. Then, brush generously with olive oil, and roast for about 20 minutes. Flip the slices and roast for another 15 minutes, until silky. Set aside.
2. Cook the potatoes in a large volume of water, until fork-tender. Or steam them (I prefer this second option). Drain, reserving ¼ cup of the cooking water. Return the potatoes to the same pot. Mash them with 2 Tablespoons of olive oil, the reserved cooking water, and season with salt and pepper. Taste for salt and adjust if needed. Set aside.

For the lentil stew and bechamel sauce:

1. Lower the oven temperature to 375°F (190°C), and grease the bottom and sides of a 9×9-inch (23 cm) baking dish or a dish of a similar size.
2. For the lentil stew. Cook the lentils with 3 times their volume of water, and bring to a boil. Reduce heat to a low, cover and simmer for 30-35 minutes until cooked through. Drain over a colander and rinse the lentils.
3. Heat 2 Tablespoons of olive oil in a large pot over medium heat. Add onions, carrots, celery, oregano, thyme, salt and pepper. Sauté for 5 to 10 minutes, until the vegetables soften up. Add the mushrooms, red wine vinegar, and sauté for another 5 minutes, until the water released by the mushrooms evaporates and they begin to brown. Add garlic and stir around for another minute. Add the lentils, crushed tomatoes, tomato paste, paprika, salt and pepper, then cover and cook for 5 minutes for the flavors to incorporate. Taste and adjust seasoning as needed.
4. For the bechamel sauce. Melt the butter in a heavy-bottomed saucepan. Stir in the flour and cook, stirring constantly, until the paste cooks and bubbles a bit, about 2 minutes (do not let it brown). Add the warm milk, and keep stirring as the sauce thickens. Bring it to a boil. Add salt and pepper to taste, lower the heat, and cook, stirring for 2 to 3 minutes more. Stir in grated Cheddar cheese during the last 2 minutes of cooking, along with a pinch of cayenne pepper. Set aside.

For assembling the vegetarian moussaka:

1. Arrange half of the eggplant slices on the bottom of the baking dish. Top with half of the lentil mixture, followed by the remaining eggplant slices and lentils. Add an even layer of bechamel sauce, then spoon the mashed potatoes on top, evening them out with a spoon into a smooth layer.
2. Bake for about 30 minutes. Remove from the oven, sprinkle with pine nuts and herbs if using, and serve. Enjoy!