Roast the walnuts in the oven at about 170 degrees for 7 minutes, then pulse-chop them in a blender.

Pulse-chop the mushrooms in two batches in a large blender.

Sauté the mushrooms over high heat with olive oil, stir a few times, then salt, stir, and set aside while keeping the pot or pan.

Finely slice the onion and sauté it with olive oil in the same pot or pan for about 10 minutes over medium-low heat.

Add the grated garlic, stir for 30 seconds, and add the tomato paste.

When the tomato paste darkens, deglaze with red wine and scrape the bottom well.

Add the mushrooms, lentils, passata, water, walnuts, salt, black pepper, thyme, and bay leaf, then simmer covered for about 20 minutes over low heat.

Stir a few times, add more water if needed, and remove the lid toward the end.

For the béchamel, melt the butter and add all the flour when it foams slightly.

Whisk with a whisk for about 2 minutes over medium heat.

Add the milk in 3 to 4 additions, whisking regularly.

Heat the oven to 180 degrees.

Add a little bolognese to the bottom of the baking dish, then layer lasagna sheets, bolognese, béchamel, and grated Parmesan until the dish is full.

Bake with aluminum foil covering the dish for the first 20 minutes.

Let the lasagna rest.