Add the diced sweet potatoes, onion, garlic, and red bell pepper to the slow cooker.
Pour in the drained black beans and the can of diced tomatoes with their juices.
Add the vegetable broth, chili powder, cumin, smoked paprika, salt, and black pepper.
Stir everything together until the spices are evenly distributed.
Cover and cook on low for 6 to 7 hours, until the sweet potatoes are fork-tender.
Taste and adjust salt or spices if needed.
Ladle into bowls and top with chopped cilantro and diced avocado before serving.