03Grease inside of a medium-size gratin dish with 1/2 tablespoon olive oil and spread a third of the onion and tomato mixture on the bottom. Begin layering zucchini in an overlapping pattern, beginning around the outside and working your way in. Sprinkle with a third of the bread crumbs. Repeat layering two more times, ending with bread crumbs. Drizzle 3 tablespoons olive oil over bread crumbs and bake for 1 to 1 1/2 hours, or until vegetables are extremely tender and top has browned.