Preheat oven to 425ºF and spray a 9x13-inch casserole dish with non-stick cooking spray. Set aside.

Heat a large nonstick skillet over medium/high heat and add olive oil.

When olive oil is fragrant, add the onion to the pan and sauté for 1 minute. Then, add the fresh spinach and toss until wilted, about 4-5 minutes.

In a large bowl, mix together the ricotta cheese, cottage cheese, sweet potato puree, minced garlic, salt, and wilted spinach. Set aside.

Spread 1 cup of marinara sauce and 0.5 cup vegetable broth in the bottom of the prepared casserole dish. Mix and spread evenly.

Stuff the jumbo shells individually with the sweet potato and cheese mixture until full. Place the shells open side up in the casserole dish.

Pour the remaining marinara sauce over the shells. Cover the casserole dish with foil and bake at 425ºF for 60 minutes.

Remove the foil and sprinkle mozzarella over the shells. Bake for another 10 minutes, or until cheese is melted.