1. Heat oven to 350 degrees . Place sweet potatoes in a medium pot and cover with water. Bring to a boil, reduce to a simmer and cook until fork-tender, about 10 minutes. Drain and return to pot over low heat. Add sugar, butter and 1/2 tsp of the salt. Mash sweet potatoes and mix until ingredients are incorporated.
2. Heat 1 tbsp of the oil in a large skillet over medium heat. Add onion and 1/2 tsp of the remaining salt; cook 5 minutes. Push onions to edge of pan. Pour in another 1 tbsp of the oil and add mushrooms. Cook 2 minutes without stirring, allowing mushrooms to brown. Mix with onions; cook 2 minutes more. Transfer to a plate.
3. Add remaining 1 tbsp oil to pan. Stir in turkey, breaking up meat with a spatula. Season with remaining 1/2 tsp salt, the garlic, smoked paprika, turmeric, cumin and chipotle. Cook 4 minutes. Stir in onions and mushrooms, tomato sauce, spinach and 1 cup water. Bring to a simmer and cook 10 to 15 minutes, until mixture thickens.
4. Spread turkey mixture into a 9 x 13-inch baking dish. Spread mashed sweet potatoes over the top in an even layer. Sprinkle with Parmesan. Bake at 350 degrees for 1 hour, uncovered.