Preheat oven to 375 degrees Fahrenheit.
Use a vegetable peeler to create long, thin ribbons from the zucchini and pat them dry with a paper towel to remove excess moisture.
Heat olive oil in a skillet over medium heat and sauté the minced garlic and ground beef until browned.
Season the beef with sea salt, black pepper, and dried oregano, then stir in the marinara sauce and simmer for 3 minutes.
In a small bowl, combine the ricotta cheese with the finely chopped fresh spinach until well mixed.
In a small oven-safe baking dish, spread a thin layer of the meat sauce on the bottom.
Layer zucchini ribbons over the sauce, followed by a layer of the ricotta-spinach mixture and more meat sauce.
Repeat the layers until all ingredients are used, finishing with a generous sprinkle of shredded mozzarella cheese on top.
Bake for 20 to 25 minutes until the cheese is golden brown and the sauce is bubbling.