Preheat the oven to 400 degrees F. Wash and dry the sweet potatoes. Prick each one several times with a fork then place on a rimmed baking sheet. Bake until soft and a fork can easily be inserted into the center of the largest one, 45 to 55 minutes.
Meanwhile, in a small bowl, stir together the chili powder, cumin, paprika, garlic powder, oregano, cayenne, salt, and brown sugar.
Spray a large nonstick skillet with cooking spray and set it over medium-high heat. Add the ground turkey and cook, breaking up the meat into crumbles as it browns, until no longer pink and cooked through, about 5 minutes. Add the spice mixture, tomato paste, and water, stirring well. Bring the skillet to a simmer, lower the heat to maintain a gentle simmer, and let cook, stirring occasionally, until the turkey meat has absorbed almost all of the liquid, about 10 minutes.
Cut the sweet potatoes open and use a fork to lightly mash the insides. Plate each potato, spoon the turkey meat evenly among them, and top each with 2 tablespoons of cheese, fresh cilantro, red onion, and/or any other toppings you like!