Bring a large pot of salted water to a boil. Add jumbo pasta shells and cook for 9-11 minutes until al dente. Drain and cool on a flat surface.

In a large mixing bowl, combine ricotta cheese, spinach, half of the mozzarella, and grated parmesan. Add garlic powder, onion powder, salt and pepper. Mix gently.

Fill each cooled pasta shell with the ricotta mixture and place in a greased baking dish.

Pour marinara sauce evenly over the shells and sprinkle with remaining mozzarella cheese.

Preheat oven to 375°F (190°C). Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 10-15 minutes until cheese is golden brown.

Let rest for 5-10 minutes before serving. Garnish with fresh herbs if desired.