Bring a pot of salted water to a boil.

Place mushrooms in a large sauté pan on high heat. Stir continuously, allowing them to release moisture.

Sprinkle salt over the mushrooms and cook until they no longer release moisture, about 5 minutes.

Stir in chopped onions and cook until the mixture is dry.

Add olive oil and sauté for about a minute. Then add garlic and cook for an additional minute.

Stir in tomato paste and cook for one minute. Reserve 1 cup of tomato sauce, and add the remainder to the mushroom mixture along with crushed tomatoes and water.

Stir in thyme, sugar, and red pepper flakes, and bring to a simmer. Reduce heat and simmer for 20 minutes.

Preheat the oven to 350°F.

Spread reserved tomato sauce over the bottom of a large casserole dish.

Cook lasagna noodles in boiling water according to package instructions until al dente, about 8 minutes. Drain and rinse with cold water.

Coat lasagna noodles with olive oil and spread them out on baking sheets to prevent sticking.

Assemble the lasagna by layering noodles, ricotta cheese, spinach, mozzarella cheese, a portion of mushroom sauce, and basil. Repeat layers.

Add a final layer of noodles and top with remaining sauce, finishing with mozzarella and pecorino cheese.

Cover with aluminum foil and bake for 25 minutes. Remove foil and bake uncovered for an additional 25 minutes.

Let lasagna rest for 10 minutes before slicing to serve.