sour cream, sliced scallions, sliced radishes, and tortilla chips, for serving
In a 4- to 6-quart slow cooker, combine the onion, bell pepper, garlic, chili powder, cumin, cocoa, cinnamon, 1 teaspoon salt, and ¼ teaspoon black pepper. Add the tomatoes (and their liquid), beans, sweet potato, and 1 cup water.
Cover and cook until the sweet potatoes are tender and the chili has thickened, on low for 7 to 8 hours or on high for 4 to 5 hours (this will shorten total recipe time).
Serve the chili with the sour cream, scallions, radishes, and tortilla chips.