Preheat the oven to 400 F.

Cook sweet potatoes in the oven for 50-60 minutes or place in the microwave for 8-10 minutes. Scrape the sweet potato into a bowl and mash with a fork until smooth. Let it cool to warm room temperature before using.

Cook the jumbo pasta shells according to package directions and drain.

Finely chop spinach.  In a medium bowl, combine the ricotta cheese, Parmesan , garlic, spinach, egg, salt and pepper, fresh lemon juice, and lemon zest. Stir well.

Stuff the cooked pasta shells with the sweet potato/ricotta mixture and place them in a lightly greased 9X13-inch baking dish (depending on how full you fill the shells, you may not use all of them). Bake the shells for 18-20 minutes, until they are hot all the way through.

Serve with your favorite marinara or Alfredo sauce.