Preheat oven to 375 degrees F (190 degrees C). Grease a 9x12-inch baking dish.
Bring a large pot of water to a boil and add zucchini slices; boil for 3 minutes. Drain.
Heat olive oil in a skillet over medium heat and cook onion and garlic, stirring frequently, until onion is translucent, about 5 minutes.
Mix bread crumbs, 1 cup Parmesan cheese, and Italian herb seasoning in a bowl.
Spoon 3 tablespoons tomato sauce into bottom of the prepared baking dish and top with 1/3 of the zucchini slices, 1/3 of the onion-garlic mixture, and 1/3 of the crumb-Parmesan cheese mixture. Repeat layers twice more, starting with 1/2 of remaining tomato sauce and layers of zucchini, onion, and crumb mixture. End with remaining tomato sauce in a layer; sprinkle 1/4 cup Parmesan cheese over the top.
Bake in the preheated oven until lasagna begins to bubble, about 30 minutes.
Preheat oven's broiler and broil the lasagna until cheese topping is browned, 2 to 3 minutes. Let casserole stand for 15 minutes to set before serving.
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