Heat the olive oil in a Dutch oven or wide pot over medium-high heat. Add the onion, bell pepper, a pinch of salt and a few grinds of pepper. Cook, stirring occasionally, until the vegetables soften, about 5 minutes. Stir in the sweet potato, garlic, chili powder and cumin and cook until combined, about 3 minutes.
Stir in the tomatoes, chili beans with their sauce and 2 cups water. Bring to a simmer and cook, stirring, until the chili thickens slightly, 10 to 15 minutes. Stir in the chicken until just heated through, about 1 minute. Remove from the heat and stir in the cilantro; season with salt and pepper. Top with chips, cheese and/or scallions.