This works amazingly all the time I have done it. Mix all the spices in the quantity mentioned below.

Peel, and Slit the karelas lengthwise as shown below. Apply light salt and keep them overnight to release bitter juices.

Preparation

1. Wash the karela lightly in the morning

2. Stuff it with light masala prepared by mixing the spices mentioned above. you can proportionate the quantity of spices based on quantity you are preparing.

3. Deep fry it to dark brown.

4.  Peel off medium onions and cut them to a ‘+’ perpendicular half slit.

Stuff the slits with masala

5. Shallow fry onions  on a slow to medium heat in  3 to 4 tbsp of oil for about 5 to 6 minutes each side. Flip only once

6. Add Deep fried karela and cook together for another 5 minutes.

and the final result