Heat a large pot or Dutch oven over medium-high heat. Add the ground beef and cook until browned, breaking it apart with a wooden spoon. Drain any excess fat.
Add the chopped bell pepper and diced sweet potato to the pot. Sauté for about 5 minutes until the vegetables just begin to soften.
Stir in the chili powder and cook for 1 minute to toast the spices, ensuring they evenly coat the beef and vegetables.
Pour in the diced tomatoes with their juices and the rinsed black beans. Stir well to combine and bring the mixture to a gentle boil.
Reduce the heat to low, cover the pot, and let it simmer for 30 to 40 minutes, stirring occasionally, until the sweet potatoes are completely fork-tender.
Ladle the hot chili into bowls and serve immediately, garnished with fresh cilantro and a dollop of sour cream or yogurt.