Lay the zucchini ribbons across paper towels. Sprinkle with 1 teaspoon of salt and let sweat for 15 minutes. Pat completely dry with fresh paper towels.

Arrange the dry ribbons on a baking sheet and bake at 400°F (200°C) for 5 minutes per side to remove residual moisture. Remove and lower oven to 375°F (190°C).

Heat olive oil in a large skillet over medium-high heat. Sauté onion and garlic for 3 minutes. Add ground beef, breaking it up until fully browned. Drain excess fat. Stir in marinara, chopped spinach, oregano, basil, and Italian seasoning. Simmer on low for 10 minutes until thickened.

In a bowl, thoroughly combine the ricotta cheese, egg, ¼ cup of grated Parmesan cheese, and 2 tablespoons of chopped fresh parsley until perfectly smooth.

In a 9x13-inch baking dish, spread ½ cup of meat sauce on the bottom. Add a layer of overlapping zucchini ribbons. Spread half of the ricotta mixture over top, followed by a ladle of meat sauce and a handful of mozzarella. Repeat the layers, finishing with zucchini ribbons, remaining meat sauce, the rest of the mozzarella, and the final ¼ cup of Parmesan.

Bake uncovered at 375°F (190°C) for 30–35 minutes until the cheese is bubbling and deeply golden-brown.

Let the dish rest on the counter for 15–20 minutes before slicing to allow the layers to fully set. Garnish with remaining fresh parsley and serve.