Preheat oven to 400 degrees F. Poke each sweet potato all over with a fork. Line a baking sheet with foil or parchment paper. Bake the sweet potatoes for approximately 40-50 minutes, or until fork tender.
During the last 10-15 minutes the sweet potatoes are baking, heat 2 teaspoons of olive oil in a large skillet placed over medium heat. Once the oil is heated, add the minced onion and cook until it has softened and the color is translucent, 3-4 minutes. Add the minced garlic and saute until fragrant, about 1-2 minutes.
Add the ground beef (or ground meat of choice), breaking it apart as it cooks, so that there are no large chunks. Add the salt, pepper, chili powder, ground cumin, and cayenne pepper. Stir to thoroughly combine the seasonings with the ground meat mixture. Cook for 5-6 minutes or until the meet is no longer pink. Add the corn to warm.
Remove the sweet potatoes from the oven and allow them to cool before handling. They will be too hot to handle and slice into to stuff right out of the oven.
While they are cooling, combine the avocado, salt, pepper, lime juice, and garlic powder into a small mixing bowl. Mash thoroughly to combine. Adjust seasonings and juice to your taste preference.
To serve, cut a slice down the center of each sweet potato and gently pull open. Fill each with a 1/4 of the taco filling, then top with mashed avocado mixture, shredded cheddar cheese, corn, and tomatoes.
Garnish with any additional toppings of your choosing!