Preheat the oven to 400°F (200°C).
Pierce the sweet potatoes with a fork a few times and place them on a baking sheet lined with parchment paper. Bake for 40-50 minutes, or until tender when pierced with a fork.
While the sweet potatoes are baking, heat olive oil in a large skillet over medium heat. Add the chopped onion and cook for about 3-4 minutes until softened.
Add the minced garlic and chopped bell pepper to the skillet. Cook for another 2-3 minutes, stirring occasionally.
Add the ground turkey to the skillet, breaking it apart with a spatula. Cook for about 6-8 minutes until the turkey is browned and fully cooked.
Stir in the cumin, chili powder, paprika, salt, and pepper. Mix well to coat the turkey and vegetables with the spices.
Add the corn kernels and diced tomatoes (if using) to the skillet. Stir and cook for an additional 2-3 minutes until everything is well combined and heated through.
Once the sweet potatoes are done baking, remove them from the oven and carefully slice them open lengthwise. Use a fork to fluff the insides.
Spoon the ground turkey mixture into each sweet potato, dividing it evenly.
If using, sprinkle shredded cheddar cheese on top of the stuffed sweet potatoes and return them to the oven for 5-7 minutes, or until the cheese is melted and bubbly.
Garnish with fresh cilantro if desired and serve immediately.