Peel the bitter gourd to remove the ridges and make it as smooth as possible. Cut into 1cm thick roundels, scoop out to make them hollow and add to a bowl. Sprinkle a generous amount of salt and 1 tsp chili powder. Shake well & keep aside.
Meanwhile, grind onions, ginger and garlic into a fine paste. Grind tomato and red pumpkin separately.
Wash the bitter gourd roundels well in running water and drain. Steam cook with a little bit of salt sprinkled over them, for about 10 minutes or till 3/4th tender. Keep aside.
Heat 2 tbsps oil in a kadhai/pan. Add jeera and let crackle. Add the onion-ginger-garlic paste along and sauté for about 2-3 minutes.
Add salt, turmeric pwder, chili powder, garam masala and let fry. Once the oil separates, add in the tomato-pumpkin gravy. Stir occasionally and let cook for 5 to 7 minutes more. Check for salt and turn off the flame once gravy is done.
For the stuffing, just keeping it simple - mix together the crumbled paneer, spinach, salt, chili powder and garam masala.
Fill this stuffing inside each steamed karela round. Heat oil for shallow frying. Gently drop in the stuffed karelas and fry on low to medium heat, on both sides till golden brown. Remove and drain excess oil.
When ready to serve, warm the gravy. Place the fried karela on the serving plates and gently pour the gravy on top or around. Garnish with coriander.