Preheat your oven to 400°F (200°C).
Wash the sweet potatoes and pierce them with a fork. Bake for 45-50 minutes or until tender.
In a large skillet, cook the ground beef over medium heat until browned. Drain any excess fat.
Add the taco seasoning and water to the skillet, stir to combine, and simmer for 5 minutes.
Stir in the black beans and corn, and cook until heated through.
Once the sweet potatoes are done, let them cool slightly, then cut them in half lengthwise and scoop out some of the flesh to create a well.
Fill each sweet potato with the taco meat mixture and top with shredded cheddar cheese.
Return to the oven and bake for 5-10 minutes, until the cheese is melted.
Top with diced avocado, a dollop of sour cream, and chopped cilantro.
Serve immediately.