Preheat the oven to 375°F (190°C). Grease a 9x9-inch baking dish with olive oil.
In a large bowl, combine the chopped spinach, ricotta cheese, feta cheese, shredded mozzarella cheese, egg, garlic powder, oregano, salt, and black pepper. Mix until well combined.
Spread a thin layer of marinara sauce on the bottom of the prepared baking dish.
Layer half of the spinach and cheese mixture over the marinara sauce.
Add another layer of marinara sauce over the spinach mixture.
Repeat the layers with the remaining spinach and cheese mixture and another layer of marinara sauce.
Top with the remaining mozzarella cheese and sprinkle with grated Parmesan cheese.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
Let the lasagna cool for 10 minutes before slicing and serving.