Preheat your oven to 375°F (190°C).

Cook the jumbo pasta shells according to package instructions until al dente. Drain and set aside.

In a large mixing bowl, combine the chopped spinach, ricotta cheese, half of the mozzarella cheese, grated Parmesan cheese, garlic powder, salt, and black pepper. Mix until well combined.

In a 9x13 inch baking dish, spread half of the basil pesto evenly across the bottom.

Fill each cooked pasta shell with a generous spoonful of the cheese and spinach mixture, then place the filled shells in the baking dish, open side up.

Once all shells are filled, spread the remaining basil pesto over the top of the shells.

Sprinkle the remaining mozzarella cheese and toasted pine nuts (if using) over the top.

Cover the dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.

Remove from the oven and let it cool for 5 minutes. Garnish with fresh basil leaves before serving.