In a heavy pot over medium-high heat, warm the oil. Add the mustard seeds and cook until they begin to pop, about 30 seconds. Stir in the cumin, dried chiles, bay leaf, onion, and garlic. Lower the heat to medium and cook, stirring frequently, until the onion has started to caramelize around the edges and soften, about 4 minutes. Stir in the paprika, turmeric, and salt and cook for 3 more minutes or until the onion is soft. Stir in the chickpea flour water, 6 cups water, and the strained tamarind water and simmer for 10 minutes. Stir in the garam masala, potatoes, and tomatoes and simmer 10 minutes longer. Add the chard and simmer until the potatoes are tender when pierced with a fork, another 10 to 15 minutes. Serve with lime wedges.