Wash karela and then using a knife or peeler, scrape the outer skin. Save the skin, as we will use it for the stuffing.
Make a slit in the karela lengthwise. Do not split in half. Now remove any large hard seeds using a spoon (you can use your fingers, but it can be harder).
Apply salt thoroughly on the inside and outside of all the karela and keep aside for at least 30 minutes. This helps to reduce the bitterness.
Add ½ teaspoon salt to the scrapings, mix well and kept aside. Let them rest for 30 minutes. (Note: using the scrapings is optional, but I like to use them in the stuffing)
Now wash karela with fresh water two to three times and squeeze them thoroughly to remove the salt and bitterness.
Wash the scrapings with fresh water two times and squeeze any excess liquid.
Heat a pan on medium heat. Add 1 tablespoon oil to it, and let it heat. If using mustard oil, heat the oil till it smokes.Now add asafoetida and scrapings (also called bhor) to the pan. Cook for about 7-8 minutes on medium heat until the color changes to dark green.
Add all the spices - salt, turmeric powder, red chili powder, coriander powder, cumin powder, fennel powder and amchur. Mix well and cook for a minute. Then turn off heat.
Using a spoon and your fingers, stuff each karela with the filling. Tie the karelas with a string. This is helpful so the filling does not fall out. If you plan to air fry, then it is okay to skip using a string.
Place the stuffed karela in the air fryer basket. Spray or brush with a little oil. Air fryer at 360°F / 180°C for about 15 minutes. Turn in between at about 9 minutes.
Heat a large heavy bottom pan on medium heat. Add oil to it, and let it heat. If using mustard oil, heat the oil till it smokes. Place the stuffed karela in the pan in a single layer. Let them cook for 2-3 minutes, then turn and cook till they brown on all sides. You can cover with a lid for faster cooking.
Once cooked, remove karela on a plate lined with paper towel. Remove the thread. Serve them as a side dish with roti and dal for a wonderful meal.