Preheat the oven to 375°F.
In a large mixing bowl, combine the chopped spinach, ricotta cheese, half of the mozzarella cheese, Parmesan cheese, marinara sauce, garlic powder, Italian seasoning, red pepper flakes (if using), egg, salt, and pepper. Mix until well combined.
In a greased 9x9-inch baking dish, spread the cooked pasta evenly across the bottom.
Pour the spinach mixture over the pasta, spreading it out evenly.
Top with the remaining mozzarella cheese and drizzle with olive oil.
Cover the baking dish with aluminum foil and bake for 25 minutes.
Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden.
Let the dish cool for about 5 minutes before serving.