Preheat your oven to 375°F.
In a small saucepan, combine the tomato puree, red lentils, and dried oregano. Simmer over low heat for 10-12 minutes until the lentils are tender and the sauce has thickened.
While the sauce simmers, place the extra firm tofu, raw cashews, nutritional yeast, lemon juice, garlic powder, onion powder, sea salt, and black pepper into a food processor. Pulse until the mixture reaches a creamy, ricotta-like consistency.
In a non-stick skillet over medium heat, sauté the sliced mushrooms and fresh spinach for 3-4 minutes until the mushrooms are soft and the spinach is fully wilted.
To assemble, spread a thin layer of the lentil marinara at the bottom of a small oven-safe baking dish. Add one sheet of brown rice lasagna noodles (break to fit if necessary), followed by a layer of the tofu-cashew ricotta and the sautéed vegetables.
Repeat the layers, finishing with a final layer of lentil marinara on top.
Cover the dish with foil and bake for 25 minutes. Remove the foil and bake for an additional 5-10 minutes until the edges are bubbling and the top is set.
Let the lasagna rest for 5 minutes before slicing to allow the layers to firm up.