Prep the veg. Peel and dice the sweet potatoes into small, even cubes.
Chop the onion and bell pepper, and mince the garlic. Smaller, uniform pieces help everything cook at the same rate.
Optional flavor boost. If you have 5 extra minutes, sauté the onion, bell pepper, and garlic in olive oil over medium heat until softened, 4 to 5 minutes. This step deepens flavor, but you can skip it if you’re short on time.
Add to the slow cooker. Combine sweet potatoes, black beans, diced tomatoes (with juices), tomato paste, onion, bell pepper, garlic, chili powder, cumin, smoked paprika, coriander, chipotle, 2 cups broth, 1 teaspoon salt, and a few grinds of pepper.
Stir and set. Mix well to distribute spices.
Cover and cook on Low for 6 to 7 hours or High for 3 to 4 hours, until sweet potatoes are tender and the chili has thickened.
Adjust consistency. Check thickness near the end. If it’s too thick, add more broth in 1/4-cup increments. If too thin, uncover and cook on High for 15 to 20 minutes to reduce.
Finish the flavor. Stir in the juice of half a lime.
Taste and add more salt, pepper, or a teaspoon of maple syrup if the tomatoes are very acidic. Add more chipotle if you want extra heat.
Serve and garnish. Ladle into bowls and top with avocado, cilantro, a dollop of yogurt or sour cream, shredded cheese, and a squeeze of lime. Crushed tortilla chips add crunch.