Preheat oven to 400 degrees F. Spray a baking sheet with non-stick cooking spray. Arrange the sweet potatoes on the baking sheet. Prick each sweet potato with a fork. Bake for 50-60 minutes in the oven, or until soft (check them after 40 minutes, pierce with a fork, and continue baking if needed).
Remove them from the oven and let cool for about 10 minutes or until safe to handle. Carefully slice them in half. Scoop out the flesh, leaving 1/4-inch thick shells, and transfer the flesh into a bowl. Set the skins aside.
Mash the sweet potatoes flesh. Add the garlic, green onion, chili powder, lemon juice, and salt to the mashed sweet potatoes and mix well.
Line the skins up on the baking sheet. Spoon the mixture into skins and top with mozzarella cheese and cilantro.
Put them back in the oven for about 15 minutes or until cheese is bubbling and starting to brown.