Rinse 2 - 3 times karonda in water to remove all the dirt and mud particles. Wash the green chili as well.
Transfer karonde and green chili in a metal colander. Let them sit in a metal colander for 10 - 15 minutes to drain all the excess water. Wipe the green chili with a clean, dry kitchen towel.
Cut each piece of karonda into two equal halves.
Cut each green chili into two to three pieces. Slit few from center lengthwise.
Heat mustard oil in a skillet over a high flame. Once the oil reaches the smoking point reduce the heat to medium.
Add cumin, fenugreek, asafoetida and carom seeds. Fry for 10 - 20 seconds.
Next add turmeric powder, coriander powder, and fennel powder. Fry for 10 seconds.
Now add chopped karonda and green chili. Stir to mix.
Season with salt and cook covered over medium heat for 5 - 6 minutes.
Open the lid, check for doneness. Sprinkle achaar masala, mix and cook uncovered for 5 more minutes. Turn off the heat.
Serve karonde mirch ki sabzi with paratha/roti. You can store it in the fridge for a week or so.