Prepare the Marinade: Grind all the ingredients listed under Marinade along with 2-3tbsp water.
Marinate the Veggies: Marinate eggplant, pepper and mushrooms in the marinade for 1 hour.
Make the Curry: Heat 2tbsp oil in a large pan; add the onions and cook until they turn golden brown on medium flame, about 8-10 minutes.
Add marinated veggies along with the marinade. Cook on medium flame for 5-8 minutes.
Then add crushed tomatoes and cinnamon stick, cook on medium-low flame, covered for 35-40 minutes or until the veggies are completely tender.
Finally add the mustard seeds, check the seasoning. Garnish with chopped cilantro and green onions. Serve with steamed rice or bread.