Cut the zucchini length wise into quarters then dice into 1/2 cubes.
Heat the oil in a deep pan. Saute the onions and garlic until soft. Add the zucchini cubes then cook until almost tender.
Puree the tomatoes, then add to the zucchini along with the the tomato sauce, paste and spices.
Cook the sauce for 45-60 minutes on medium heat. Taste and adjust the seasonings.
Shred the cheese and set aside.
In an lasagna pan, place a bit of the sauce on the bottom. Add the lasagna sheet, cutting to fit, then layer the 1/4 of the sauce, sprinkle 1/4 of the Parmesan cheese, dollops of 1/4 of the ricotta cheese (if using), then top with 1/4 of the shredded cheese.
Repeat 3 more times.
Bake for approximately 45 minutes uncovered until the dish is hot and the cheese is melted.