While the eggplant is cooking, spray a saute pan with cooking spray on medium. Add the onion and cook for about 3 minutes. Add the zucchini and garlic and cook for another 5-7 minutes until cooked through.
Cover the bottom of your baking dish with 1 cup of marinara sauce. Then begin assembling the rollatini and placing in the baking dish. To assemble, take one eggplant and place a heaping tablespoon of the zucchini mixture at one end. Roll tightly and continue until all of the eggplant is rolled.