Sauté the mushrooms and garlic over medium heat until tender; cover between stirring to keep them from drying out. Remove from heat and add the spaghetti sauce.
Place the tofu and thawed spinach in the food processor (or blender, or hand-mash) and process briefly. Add the remaining filling ingredients to the processor and blend until smooth.
Preheat the oven to 375 degrees.
Spread half of the sauce in the bottom of a 9×12-inch pan. Place a layer of noodles over the sauce. Spread half of the tofu mixture on the noodles. Cover with another layer of noodles and then spread the remaining tofu mixture over them. Top with a final layer of noodles, and pour the remaining sauce over this. Cover the dish tightly with foil, and bake for 30 minutes. Then, remove the foil and bake for another 30 minutes. Remove from the oven and sprinkle with sliced black olives.