Chili "Meat": Add walnuts, mushrooms, and drained beans to a food processor. Blitz until mostly broken down into a chunky paste, scraping down the sides as needed.
Cook Veggies: Heat oil over medium in a large pot. Add onion, garlic, and sweet potato, cooking until onion is translucent and soft, about 10 minutes.
Cook "Meat": Add chili "meat" then continue to cook for 5 minutes, stirring occasionally.
Bring It Together: Add diced tomatoes (undrained), black beans (drained), 1 cup of the vegetable broth, and all seasonings. If your chili is thick, add remaining ½ cup of broth.
Simmer: Cover and let simmer for 30 minutes, stirring occasionally, until consistency is thick and chili-like (too watery? let it simmer with the lid off).
Serve: Ladle into bowls, optionally topping with sour cream/yogurt, cheese, tortilla chips, or green onions.
Notes
Store in an airtight container in the fridge for 4 to 5 days.