In a large pot, combine the red onion, carrots, celery, bell pepper, and garlic. Stir in the tomatoes, mushrooms, bay leaves (if using), kombu (if using), parsley, and pippali. Add the water and bring to a boil. Lower the heat to low and simmer for 1½ hours. Remove from the heat, let cool slightly, then remove and discard the bay leaves and kombu (if used).