Begin by bringing a large pot of salted water to a boil. Carefully add the jumbo pasta shells and cook until al dente, about 8 to 10 minutes. Drain and set aside.

In a mixing bowl, combine the ricotta cheese, shredded mozzarella, grated Parmesan, and egg. Stir until smooth and creamy.

Heat olive oil in a skillet over medium heat. Add minced garlic and sauté for 30 seconds. Add spinach and cook for 2 to 3 minutes until wilted. Remove from heat and mix into cheese filling.

Add Italian seasoning, along with salt and pepper to taste to the filling. Stir thoroughly.

Preheat your oven to 375°F (190°C).

In a baking dish, spread marinara sauce across the bottom. Fill each pasta shell with the spinach and ricotta filling and arrange in the dish. Top with remaining marinara and mozzarella.

Cover with foil and bake for 20 minutes. Remove foil and bake for another 10 minutes until cheese is bubbly.

Let rest for a few minutes before serving. Garnish with fresh basil if desired.