Preheat your oven to 375°F (190°C).
Slice the zucchini into long, thin planks using a mandoline or sharp knife, then pat them dry with paper towels to remove excess moisture.
In a medium mixing bowl, whisk the egg and then stir in the ricotta cheese, parmesan, dried oregano, garlic powder, sea salt, and black pepper until well combined.
Spread 2 tablespoons of the marinara sauce across the bottom of a small individual baking dish.
Place a layer of zucchini planks over the sauce, followed by a layer of the ricotta mixture and a handful of fresh baby spinach.
Repeat the layers until all ingredients are used, ending with a final layer of marinara sauce.
Sprinkle the shredded mozzarella cheese evenly over the top.
Cover the dish with foil and bake for 20 minutes.
Remove the foil and bake for an additional 10 to 15 minutes until the cheese is melted and the edges are bubbling.
Let the lasagna rest for 5 minutes before slicing to allow the layers to set.