Soak chhole in lukewarm water for 6-7 hours. Add chhole, 3-4 cups water, salt and rose petals. Cover the lid and cook it until 8-10 whistles on medium to low flame or until it tender. Once done remove from gas. Now assemble all gravy ingredients. Cut onion, ginger and garlic. Grind into a smooth paste. Grind tomatoes and green chillies separately. Keep it aside.