Preheat the oven to 400°F (200°C). Wash the sweet potatoes and pierce them a few times with a fork. Bake directly on the oven rack for 45-50 minutes, or until tender when pierced through with a knife.

While the sweet potatoes bake, prepare the filling. Heat a medium skillet over medium heat. Add the corn, black beans, red onion, and taco seasoning. Cook for 5-7 minutes, stirring occasionally, until the corn is slightly charred and the mixture is heated through.

Once the sweet potatoes are cooked, remove them from the oven and let them cool slightly. Cut each potato in half lengthwise and carefully scoop out some of the flesh, leaving a 1/2-inch border. You can mash up the scooped-out flesh and add it to the filling if desired.

Fill each sweet potato half with the black bean and corn mixture. Top with diced tomatoes and avocado slices. Drizzle with vegan ranch dressing to taste.