Preheat oven to 400 degrees.
Trim zucchini and cut each in half crosswise. Cut each half lengthwise into 4 slices. Arrange alternating slices of zucchini and tomato in a 12-by-9-inch gratin dish; drizzle ¼ cup olive oil on top. (The gratin can be prepared to this point up to a day in advance, covered and refrigerated.)
For the topping: Combine cheese, bread, oregano, salt and pepper in a food processor; process until bread is in small crumbs. Transfer to bowl and stir in olive oil (I just add oil to the breadcrumbs in the processor and pulse to combine.) Sprinkle topping over vegetables. Bake 35 minutes, or until vegetables are tender and moist and the topping is nicely browned.
