To make pickle spice, Dry roast these spices and grind to a fine paste.
2 tsp coriander seeds, 1 tsp cumin seeds, 2 tsp fennel seeds, 1/2 tsp yellow mustard halves, 1/4 tsp fenugreek seeds, 1/4 tsp (pinch) onion seeds (optional).
Add 3 - 4 tbsp ready to use curry paste (refer link in text), 2 tbsp pickle spice mix, salt and dry mango/ aamchur in a mixing bowl and mix well all ingredients
Wash and peel the skin of the bitter gourd. Make slits vertically from one side. Carefully do this to make a pocket only to stuff the masala mix.
Stuffing the Karela
Take one spoon of mixture and try to fill as much enters into it. Repeat for all and keep aside on a plate.
Take a small thread and try to tie the karela as shown in picture.
The idea is to seal the karela so that the masalas won't come out while frying. Some excess masala will come out in this process. But don't worry about it.
Stir-frying the stuffed karels
Heat 5 - 6 tbsp oil and once oil is hot place stuffed karela into the pan. cover with lead and cook on medium low heat. Occasionally flip the karela with help of a tong.
If you have more quantity karela then do it in batches of 5 - 6 at a time. Don't over crowd the pan. It takes 8 - 10 minutes on low flame to cook the stuffed karela completely. If you have more in quantity or in large size karela then it might take bit longer to cook the whole lot.