Preheat your oven to 375°F (190°C). Lightly grease a medium baking dish with a little olive oil to prevent sticking.
Slice the zucchinis into rounds about 1/4 inch thick and place them in a large mixing bowl. Try to keep the slices uniform so they cook evenly.
Drizzle 2 tablespoons of olive oil over the zucchini slices. Add the minced garlic, dried oregano, salt, and pepper. Toss gently with your hands or a spoon until all slices are evenly coated.
In a separate small bowl, combine 1 cup shredded mozzarella, 1/2 cup grated Parmesan, and 1/2 cup breadcrumbs. Mix briefly so the cheeses and crumbs are evenly distributed.
Arrange a single layer of zucchini slices across the bottom of the prepared baking dish, slightly overlapping if needed. Sprinkle a generous layer of the cheese-and-breadcrumb mixture over the zucchini. Repeat layering with the remaining zucchini and topping until the dish is filled and the last layer is covered in the cheese mixture.
Place the baking dish in the preheated oven and bake for 20 to 25 minutes. You want the zucchini to be tender when pierced with a fork and the cheese to be golden and bubbly. If the top browns too quickly, loosely cover with foil for the remaining cook time.
Once baked, remove from the oven and let the dish rest for 5 minutes. Garnish with fresh basil if desired, then serve warm straight from the dish.
Notes
For best texture, reheat in a 350°F (175°C) oven for 10 to 15 minutes until warmed through and the top crisps again.