Place the mushrooms, walnuts, and zucchini in a food processor. Pulse a few times until the mixture is very finely chopped. Transfer to a bowl. Repeat this process with garlic, onion, and carrots.
Heat butter or olive oil over medium high heat. Add your chopped veggies along with the spices. Sauté for 7-10 minutes until very soft and fragrant. Add tomato sauce and salt; stir to combine. Taste and adjust! Your seasoning amounts will depend on your brand of sauce.
Preheat the oven to 400 degrees Fahrenheit. Mix mascarpone cheese with grated garlic and salt.
Start with spreading a layer of sauce in the bottom of a 9x13 pan. Then, layer in the following order for each layer: a few noodles, 1 cup sauce, a few dollops of mascarpone, 1/2 cup Parmesan, 1/2 cup mozzarella, and repeat (I usually get 4 layers out of this amount). End with noodles, sauce, cheese, and dollops of extra sauce on top to make it pretty.
Cover with foil and bake for 40-45 minutes. Remove foil and broil for 5 minutes to get the cheese browned on top. Let stand for 10 minutes or so, then cut and serve!