Put yellow onion, chili powder, tomato paste, water, oregano, cumin, and salt in a microwave safe bowl. Put in microwave for 5 minutes, stirring occasionally, until onions are soft.
Transfer to a slow cooker.
Stir in beans, 9 cups of water, soy sauce and mushrooms. Cover and cook on high for 8-10 hours, until beans are tender.
Put bulgar and 2 cups of water in a microwave safe bowl. Cover the bowl and cook the bulgar in the microwave and cook for about 5 minutes, until bulgar is softened.
Drain the bulgar and stir into the chili.
Cover the chili and cook on high, until bulgar is tender, 5 to 10 minutes.
Add more water to the chili if needed and season with salt and pepper to taste.
Serve with optional toppings of red onion, green onions, cilantro or avocado.