Preheat oven to 400°. In a large pan over medium-high heat, sauté the onion in the olive oil for about 5 minutes, until it begins to brown. Add the garlic and mushrooms, and allow to cook for about 10 more minutes, until the mushrooms release their liquid and are fragrant. Mix in the kale and cook until it wilts.
Spoon 1/3 of the tomato sauce over the bottom of a 9”x12” baking or casserole dish. Carefully place a layer of polenta on top of the sauce. If it’s difficult to handle, cut it into four smaller pieces.
Spread the tofu ricotta over the polenta, and top it with the vegetable mixture. Evenly pour 1/3 of the tomato sauce over the veggies.
Carefully place the second layer of polenta on top of the lasagna, again cutting it into four pieces if necessary. Top with the rest of the sauce.
Bake for 30-40 minutes, until the edges of the polenta begin to brown and the sauce is bubbly.
Let stand for 5 minutes before serving. Serve hot.