Preheat oven to 350 degrees F (176 C) and use a mandolin or sharp knife to very thinly slice the peeled sweet potato and butternut squash.
Add sliced potatoes and squash to a large mixing bowl and top with oil, rosemary, thyme, parsley, nutritional yeast, salt, and garlic. Toss to combine.
Add to a 9x13-inch (or similar size - mine was slightly smaller // adjust if altering batch size) baking dish in a single layer, trying to arrange the potatoes and squash in layers like lasagna. Press down to flatten. Then cover with foil.
Bake for 40 minutes. Then remove foil and bake for another 10-15 minutes at 375 degrees F (190 C) or until the potatoes and squash are fork tender and slightly golden brown on the edges.
Let cool briefly. Then serve with fresh herbs and a sprinkle more nutritional yeast or vegan parmesan cheese (optional).
Store leftovers loosely covered in the fridge up to 3 days or in the freezer up to 1 month. Reheat in the microwave or a 350-degree F (176 C) oven until hot.
*To keep this recipe oil-free, I would recommend modifying this recipe for Sweet Potato Lasagna (and omit the oil). The tofu acts as an egg replacer and allows you to cut down on, or completely omit the oil. *Nutrition information is a rough estimate calculated with the lesser amount of oil (4 Tbsp as recipe is written) and without the vegan parmesan cheese. *This recipe is inspired by a Spanish-style tortilla, minus the egg. Think of it somewhere between a gratin and a frittata. If you want more "egg" texture, feel free to add some tofu to act as an egg, such as in this recipe.