To prepare the stuffing, add little oil in a hot pan, and put some cumin seeds. When the cumin seeds splutter, add chopped onions and sauté. Add pinch of hing, salt, turmeric and mix. When the onions are slightly cooked, add amchur powder, chilli powder and garam masala. Mix all ingredients well. Add some green peas and mix. Add boiled mashed potato (there should not be any moisture in the potato mash). Mix well, switch off the flame and allow this mixture to cool. For the outer casing, combine besan atta (chickpea flour), salt and baking soda in a bowl. Add little by little water and make this mixture into a thick paste free of lumps. Slit the green chillies, remove seeds and keep aside. Stuff the green chillies with the potato mix. Dip the stuffed green chillies in the chickpea batter till they are completely covered. Heat oil in a pan and when the oil is hot, gently drop the coated green chillies and fry on medium heat until they turn slightly golden brown in colour. Remove and place onto a plate. Cut them into small pieces and sprinkle them chaat masala on the cut mirchi. Serve hot with sweet chutney.