Preheat the oven to 375°F. Lightly oil a deep 2 1/2- to 3-quart baking dish (about 9 by 12 inches).

In a small bowl, combine the extra-virgin olive oil and garlic.

Bring a large pot of salted water to a boil and prepare a bowl of ice water. Plunge the spinach into the boiling water for about 15 seconds, then drain and transfer to the ice bath. When cool, drain again and squeeze dry. Chop coarsely and transfer to a bowl.

Trim the ends of the zucchini, then cut lengthwise into 1/4-inch-thick slices. Put in a separate bowl.

Cut the potatoes in half lengthwise, put the halves cut side down, and then cut them lengthwise into 1/4-inch-thick "fingers." Put the potatoes in a third bowl.

Season the spinach, zucchini, and potatoes lightly with salt (the Parmesan will add more salt) and with pepper. Toss the vegetables with some of the garlic oil, using enough to coat them generously. Reserve any remaining oil for drizzling on top of the tiella.

Using half of the potatoes, make a layer in the prepared baking dish, filling in any gaps with small pieces. Spread with 1/2 cup of the tomato sauce, then sprinkle with 1 1/2 tablespoons of the basil, 2 tablespoons of the Parmesan, and 2 tablespoons of the bread crumbs. Repeat the layering?vegetable, tomato sauce, basil, Parmesan, bread crumbs?using all the zucchini and then all the spinach. Top with the remaining potatoes and then the remaining tomato sauce and basil. Drizzle with the remaining garlic oil.

Cover and bake until tender and bubbling, about 1 1/4 hours. Uncover, sprinkle with the remaining 2 tablespoons Parmesan and the remaining 4 tablespoons bread crumbs, and continue to cook until the top browns, about 15 minutes longer. Remove from the oven and let cool to room temperature to allow the dish to settle and deepen in flavor.

Tiella may be served hot, warm, or at room temperature. Reheat in a low oven if desired. To serve, cut into squares and carefully lift out of the pan with a spatula.