Preheat your oven to 400°F (200°C). Wash the sweet potatoes thoroughly and pierce them several times with a fork. Place them on a baking sheet and bake for 45-60 minutes, or until tender.
While the sweet potatoes are baking, heat the olive oil in a large skillet over medium heat. Add the diced onion and cook until translucent, about 5 minutes. Stir in the minced garlic and cook for an additional minute.
Add the ground turkey to the skillet, breaking it apart with a spatula. Cook until browned and cooked through, about 7-10 minutes. Drain any excess fat.
Stir in the taco seasoning, black beans, corn, and diced tomatoes. Cook for another 5 minutes, allowing the flavors to meld. Season with salt and pepper to taste.
Once the sweet potatoes are done, remove them from the oven and let them cool for a few minutes. Slice each sweet potato down the middle, creating a pocket.
Spoon the turkey mixture into each sweet potato, packing it in generously. Top with shredded cheddar cheese and return to the oven for an additional 5-10 minutes, or until the cheese is melted.
Remove from the oven and garnish with fresh cilantro. Serve with sour cream or Greek yogurt if desired.