Preheat the oven to 400 F and line a baking sheet with parchment paper.
Cut the sweet potatoes in half on lengthways and place them (cut size up) on the baking sheet.
Roast for about 15-18 minutes, or until fork tender. Turn off oven.
Meanwhile, heat the oil in a large skillet. Add the onion, garlic, and bell pepper and sauté for about 4 minutes.
Add in mushrooms, and cook until tender, 6-7 minutes.
Stir in the corn, black beans, tomato paste, cumin, and chili powder and cook for 2-3 more minutes.
Remove the sweet potatoes from the oven and top them with the Mexican mixture, then add mashed avocado and a tablespoon of yogurt on top of each.
Garnish with fresh cilantro and enjoy!