In a large skillet, heat oil over medium heat. In hot oil, cook cumin seeds, garam masala, cardamom, cayenne pepper, mustard seeds, salt, and garlic. When seeds start to pop, stir in chicken and potatoes. Cook for 15 minutes, or until chicken is nearly done.
Stir in tomatoes, chard, and yogurt. Cover, and cook 15 minutes more, or until potatoes are tender and chicken is cooked through.
