Place the thinly sliced onions in a small bowl. Add lime juice, zest, honey, and a pinch of salt. Toss everything together and let sit while you prepare the chili.
Heat olive oil in your pot over medium heat. Add sliced garlic and cook until lightly golden and fragrant, about 1 minute. Stir in tomato paste, smoked paprika, cumin, and chipotle paste with a splash of water for 2 minutes to make a rich paste.
Toss the diced sweet potatoes into the spice mixture. Pour in diced tomatoes and broth, stir, cover, and simmer on medium-low for 20–22 minutes until tender. Add extra broth if it becomes too thick.
Combine Greek yogurt, cilantro, avocado, salt, pepper, and lime juice in a blender. Blend until smooth and adjust seasoning to taste. This adds a creamy, fresh contrast to the smoky chili.
Stir in the black beans with their liquid and simmer uncovered for 4–5 minutes. Taste and adjust salt and pepper. Adding beans last keeps their texture intact and earthy flavor pronounced.
Spoon chili into bowls, drizzle with herby yogurt, and scatter pickled onions on top. Serve with rice or tortillas and sprinkle with cheddar and cilantro if desired.