1. Preheat oven to 400 °F (200°C).
2. Pierce one sweet potato with a fork on all sides multiple times and microwave on high or 8 minutes or until fork-tender. Let cool and remove skin. Add to a large bowl and mash potato.
3. Add ricotta and nutmeg to sweet potato mash and mix thoroughly. Set aside.
4. In a large pan over medium-high heat, add 1 Tbsp (15 mL) canola oil. Add onion and sauté for 5-7 minutes until soft and slightly golden. Add garlic and dried sage, cooking for another 1-2 minutes.
5. Remove casing from sausages and crumble into pan. Cook with onion mixture for 10-12 minutes or until meat is cooked through. Add 2 cups (500 mL) of kale and wilt, about 1 minute. Remove from heat and set aside.
6. Using a mandolin, slice one sweet potato lengthwise. Slices should be about 1/8-inch (3 mm) thick. Set slices aside for assembly.
7. Cut apples into quarters and remove core. Using the mandolin slice apple quarters into thin slices, about 1/8-inch thick (3 mm). Set aside.

Assembly

1. Spray a 9×13-inch (23×33 cm) baking dish with canola cooking spray. Line the bottom with slices of sweet potato. Top sweet potato slices with ½ the ricotta mixture and spread evenly using a rubber spatula. Using 1⁄2 of the apple slices, top ricotta mixture with an even layer. Spread  ½ of sausage mixture over top and sprinkle with 1⁄2 of grated parmesan. Repeat each layer one more time.
2.  In a small bowl, toss remaining kale with 1 Tbsp (15 mL) canola oil. Distribute evenly on top of lasagna.
3. Cover with tin foil and bake for 40 minutes. After 40 minutes remove tin foil and continue to cook for 10-15 minutes or until kale leaves are browned.
4. Allow to cool before serving.