If you are preparing your own sauce, begin by adding all the sauce ingredients to a pot and simmer until the onions are thoroughly cooked.
Defrost frozen spinach and add to the sauce when the sauce is cooked. Continue cooking until it begin to boil, then remove from the heat.
Place the tofu, lemon juice, nutritional yeast and cornstarch in a food processor and blend at high speed until creamy smooth.
While the sauce is cooking, boil the lasagna in a separate pot until tender. Drain and spread on wax paper to dry.
In a large, sprayed baking dish, place a layer of the spinach and sauce, then place a layer of lasagna, followed by a thin layer of the tofu cream. Repeat making successive layers in the same order until all the ingredients are used or until the baking dish is full. Try to have at least three sets of layers.
Bake in the oven at 350 degrees for 30 - 45 minutes. Remove, let cool for about 10 minutes before cutting and serving.