Preheat the oven to 375 degrees. Spray a 9×13" baking dish with cooking spray and pour 1/2 of the marinara sauce into the bottom of the prepared baking dish and spread evenly. Set aside.

Heat the olive oil in a large skillet over medium heat. Add the garlic and cook 30 seconds. Add the baby spinach and cook until wilted, about 2 minutes and remove from heat.

Place the spinach mixture in a fine mesh sieve and squeeze to remove excess liquid with your hands or wrapped in a towel. Place on a cutting board and chop well.

Place the ricotta cheese and egg in a medium bowl and mix well to combine. Stir in 1 cup of the mozzarella cheese, parmesan cheese, 1/4 teaspoon of salt and 1/8 teaspoon black pepper. Add the spinach and mix well to combine.

Open each shell and stuff well with the ricotta mixture, then place in the marinara sauce in the baking dish. Top with the remaining marinara sauce and mozzarella cheese.

Coat a sheet of foil with cooking spray or oil and place over the top of the baking dish (this will keep the cheese from sticking to it). Bake covered for 20 minutes, then remove the foil and bake for 10 minutes more or until golden brown. Cool for 10 minutes, then serve and enjoy!