1. To make Filling: Preheat oven to 375°F. Heat oil in skillet over medium-high heat. Sauté onions and garlic in oil 4 to 5 minutes, or until golden. Add spinach, and cook 2 to 3 minutes, or until wilted. Transfer spinach mixture to bowl of food processor. Add tofu, cream cheese, basil, and nutritional yeast, and purée until mixture is thick and smooth. Season with salt and pepper, if desired.
2. Spread one-quarter of Speedy Red Sauce recipe on bottom of 13- x 9-inch baking dish. Cover with one-third of noodles (4 or 5 noodles), then half of Filling, and ladle on another one-quarter of sauce. Repeat layer of noodles and remaining Filling. Spread sausage evenly over top, and top with one-quarter of sauce. Finish with final layer of noodles and remaining sauce. Sprinkle with shredded cheese.
3. Cover lasagna with foil, and bake 30 minutes, or until bubbling hot. Uncover, and bake 15 to 20 minutes more, or until noodles are tender and topping is melted. Remove from oven, and let stand 10 minutes before serving.