Preheat the oven to 450 degrees F (230 degrees C).
Arrange the Zucchini (2 pound) in single layers on two Silat or parchment-lined rimmed sheet pans. Season with Kosher Salt and Freshly Ground Black Pepper (to taste) on each side, drizzle each pan with Extra-Virgin Olive Oil (2 tablespoon), toss to coat, then spread into an even layer.
Roast for 10 minutes. Remove pans from oven and set aside.
Reduce oven to 400 degrees F (200 degrees C).
Meanwhile, make the breadcrumb topping: In a food processor, pulse enough Bread (to taste) to make 1 cup of breadcrumbs. Toss the breadcrumbs with the Parmigiano-Reggiano (1/4 cup), Extra-Virgin Olive Oil (2 tablespoon), Salt and Pepper (1/2 teaspoon). Set aside.
Into a circular gratin dish or a 9x9-inch similar baking pan, spoon a small amount of Tomato Sauce (to taste), about a heaping 1/3 cup, then add a thin scattering of Parmigiano-Reggiano (3/4 cup), then a single layer of zucchini, shingling the slices slightly. Repeat until all ingredients are used, ending with a little sauce and cheese.
Top with the breadcrumb mixture. Bake until the mixture is bubbly and top is golden, 25 minutes or so depending on size of pan and thickness of layers.
Remove from heat and allow to rest for 10 minutes before serving. This also tastes great at room temperature.