Boil a large pot of hot water. Add in the pasta and cook until al dente (tender but still firm). Pour into a strainer and rinse under cold water. Set aside.
Heat a pot over medium high heat with the olive oil. Cook the garlic for 1-2 minutes, then stir in the spinach. Cook until it becomes wilted. Let the spinach garlic mixture cool for 10 minutes before moving onto the next step.
In a bowl, combine the cooled spinach, ricotta cheese, mozzarella cheese, grated parmesan, eggs, salt and pepper. Mix everything together.
Pour half of the marinara sauce into a 9x13 baking dish. Use a spoon to fill each jumbo shell with the spinach cheese filling. Place in a single layer on top of the sauce. Repeat until all the filling has been used up.
Pour the last half of the sauce overtop of the pasta. Cover the baking dish with foil and bake for 25 minutes. Remove the foil and bae for 12-15 minutes longer, until sauce is bubbling and cheese has melted. Sprinkle more mozzarella cheese on top and serve.