Begin by slicing the zucchini into 1/4-inch rounds. Sprinkle the slices with salt and place them in a colander for 20 minutes; this helps remove excess moisture. Once time’s up, pat the zucchini completely dry with paper towels.

In a large skillet, heat a drizzle of olive oil over medium heat. Add the diced onion and minced garlic, cooking until the onion is soft—about 3 to 5 minutes. Next, stir in the fresh baby spinach and sauté until wilted, roughly 2 to 3 minutes.

In a mixing bowl, whisk together large eggs, heavy cream, and your favorite herbs until well combined. Gently fold in crumbled feta cheese.

Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish with olive oil. Layer half of the zucchini slices, then add the sautéed spinach mixture evenly. Pour half of the custard over the spinach layer followed by the rest of the zucchini.

Place the baking dish in the preheated oven and bake for 35 to 45 minutes, or until the top is golden and bubbly. Switch to broil for the last 2 minutes.

Once your casserole is beautifully bubbly and golden, remove it from the oven and allow it to cool for about 10 minutes before serving.