Preheat oven to 350 degrees F.
Heat 4 tbsp of butter in a sauté pan and cook mushrooms until tender, add chopped basil, set aside. Heat 2 tbsp of butter in sauté pan, add shallots and garlic, and cook until translucent. Add mushrooms, 2 tbsp of parmesan cheese, and season to taste with salt and pepper.
In a bowl, combine ricotta cheese, grated lemon rind, and parsley. Season to taste with salt and pepper.
Butter an 8"x 8" baking pan and fill with alternate layers of lasagna, mushroom mixture, and ricotta mixture, finishing with a layer of lasagna.
Cover with mozzarella cheese and sprinkle with additional parmesan. Bake 30 minutes, or until golden brown. Serve garnished with thyme.