Step 1

Heat oil in a large stock pot or Dutch oven over medium-high heat until shimmering. Add onions, carrot, celery, bell pepper, chili powder, cumin, coriander, oregano, thyme, chipotle chili powder (if using), 1/2 teaspoon salt, and 1/4 teaspoon pepper. Cook until vegetables have softened, 7 to 10 minutes.

Step 2

Stir in garlic until fragrant, about 30 seconds. Stir in sweet potatoes, black beans, tomato puree, diced tomatoes and their juice, and water. Bring to a simmer, cover, and cook until the sweet potatoes are tender and starting to break down, about 30 minutes.

Step 3

Remove lid and continue to simmer until slightly thickened, about 30 minutes longer. Simmer longer for a thicker sauce. Season to taste with salt and pepper. Serve avocado, cilantro, and scallions if desired.