Prep the veggies. Peel and cube the sweet potatoes. Dice the onion and bell pepper, and mince the garlic. Aim for even sizes so everything cooks at the same pace.
Layer in the slow cooker. Add sweet potatoes, black beans, tomatoes with juices, onion, bell pepper, and garlic to the crockpot.
Add liquids and seasonings. Stir in vegetable broth, tomato paste, chili powder, cumin, smoked paprika, coriander (if using), chipotle or cayenne, salt, and pepper.
Add olive oil if you want a silkier finish.
Cook low and slow. Cover and cook on Low for 6–8 hours or High for 3–4 hours, until the sweet potatoes are tender and the flavors are well blended.
Finish with lime. Stir in lime juice to brighten the chili. Taste and adjust salt, pepper, and heat as needed.
Serve with toppings. Ladle into bowls and add your favorite toppings for freshness and texture.