Preheat oven to 375°F (190°C).

Cook jumbo shells in salted boiling water until al dente. Drain and set aside.

In a large bowl, mix spinach, artichokes, ricotta, mozzarella, Parmesan, garlic, Italian seasoning, salt, and pepper until well combined.

Spread 1 cup marinara sauce in the bottom of a baking dish.

Stuff each shell generously with the cheese mixture and place in the dish.

Spoon remaining marinara over shells and sprinkle with additional mozzarella.

Cover with foil and bake for 20 minutes.

Uncover and bake an additional 10 minutes until bubbly and lightly golden.

Let rest 5 minutes before serving.