In a saucepan over medium heat, combine the water, red onion, and bell pepper, then cook, stirring, for 5 minutes, or until the vegetables are tender. Add the tomato sauce, chili powder, black cumin, oregano, garlic powder, onion powder, pippali, and sodium-free salt substitute (if using), and stir to blend. Cook for 10 minutes, stirring occasionally. Remove from the heat, stir in the miso paste, and set aside to cool slightly. Transfer the sauce mixture to a blender or food processor and process until smooth. Set aside.