Place a rack in the upper third of the oven and preheat the oven to 350°F (175°C). Grease a 9-inch (22.5 cm) pie pan with olive oil. Dust the pan with breadcrumbs and tap out any excess crumbs.

In a large skillet, heat 3 tablespoons olive oil over medium heat. Add the onion and cook, stirring occasionally, until very soft and fragrant, 8 to 10 minutes. Transfer the onion to a large plate or tray and set aside.

Increase the heat to medium-high, and if the pan seems dry, add another ½ tablespoon olive oil. Add the zucchini, sprinkle with salt, and sauté until the zucchini slices have softened a bit but are not completely cooked through, about 5 minutes. Transfer the zucchini to the plate with the onions and let cool for about 10 minutes.

In a large bowl, stir together the eggs, yogurt, the ½ cup (50 g) grated cheese, and the milk until smooth. Stir in the flour and season the mixture with 1 teaspoon salt and a few twists of black pepper. Fold in the dill, onion, and zucchini, mixing well.

Pour the mixture into the prepared pie pan, smoothing the surface so the zucchini slices lie flat. Sprinkle with the 2 tablespoons breadcrumbs and the remaining 2 tablespoons cheese.

Bake the pashtida until firm and golden brown, 55 to 65 minutes. If you like, turn on the broiler and cook for a few more minutes for a crispy golden-brown surface. Remove from the oven.

Let the pashtida cool for a few minutes before serving warm, or let cool completely and serve at room temperature.