Slice zucchini into 1/2-inch thick slices and then quarter each slice. You should have a little over 6 cups or 600–700g of quartered/chopped zucchini. Sprinkle lightly with salt (reserve the 1/4 teaspoon of salt for step 3… this is just a light sprinkle). Line a colander with a clean kitchen towel or paper towels. Place zucchini in lined colander. Let sit for just 10 minutes. Blot dry as best you can.

Preheat oven to 400°F (204°C). Grease a 2.5-quart baking dish. (See Note below for recommendations on best pans to use.)

In a large bowl, whisk the heavy cream and egg together. Stir in the the onion, garlic, salt, pepper, oregano, thyme, basil, feta cheese, and 3 Tablespoons (21g) breadcrumbs. Stir in the zucchini. Spread mixture into prepared baking dish. Top evenly with remaining breadcrumbs.

Bake, covered lightly with aluminum foil, for 25 minutes. Uncover and sprinkle with 2 Tablespoons parmesan cheese or crumbled feta cheese. Return to the oven, uncovered, and bake for 5 more minutes or until zucchini is tender. For a crispier/browner top, switch the oven to broil and broil for the last 30 seconds. (If skipping the cheese topping, you still want to bake the dish for 5 minutes uncovered.)

Remove from the oven and sprinkle lightly with red pepper flakes, if desired. Leftovers keep well in the refrigerator in an airtight container for up to 5 days. Reheat as desired.