Preheat oven to 375°F. Lightly grease a 9×13-inch baking dish.

Cook pasta shells according to package directions until al dente. Drain and toss with a little olive oil to prevent sticking.

In a skillet over medium heat, sauté minced garlic in 1 tsp olive oil for 1 minute. Add spinach and cook until wilted, about 3 minutes. Remove from heat, drain, and chop once cooled.

Spread marinara sauce across the bottom of the baking dish.

In a large bowl, combine ricotta, 2½ cups mozzarella, Parmesan, Italian seasoning, egg, salt, pepper, and the chopped spinach. Mix well.

Fill each pasta shell with the ricotta mixture (about 2 tablespoons per shell) and place in the baking dish over the sauce.

Sprinkle remaining ½ cup mozzarella over the top.

Cover with foil and bake for 20 minutes. Remove foil and bake for 5 more minutes until cheese is melted and bubbly.

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