In a bowl combine gram flour with chopped onion. Season with salt, coriander powder, cumin seeds, chaat masala, chopped green chillies, and yogurt. Mix well. Add mustard oil and knead to prepare the dough for the roti. Keep the dough aside for 15 min. Pinch small balls from the dough. Press and flatten each ball using a rolling pin to make roti. Heat a pan and cook the roti on both sides. Apply little ghee on both sides while roasting. Garnish besan masala rotis with coriander sprig and serve the hot with pickle.