Preheat the oven to 400°F (200°C). Pierce the sweet potatoes with a fork, place them on a baking sheet, and bake for 45-60 minutes or until tender.
Meanwhile, heat olive oil in a large skillet over medium heat. Add onions and garlic, sautéing until fragrant.
Add bell pepper, cooking for an additional 5 minutes. Stir in black beans, kidney beans, diced tomatoes, chili powder, cumin, salt, and pepper. Simmer for 15-20 minutes.
Once the potatoes are done, slice them open and stuff with the chili. Top with avocado, yogurt, and cilantro, if desired.
Notes
Optional toppings include: Greek yogurt or sour cream, cilantro, green onions, avocado, cheese, and salsa.