Wash arbi thoroughly and then cook it in pressure cooker on low flame for 4-5 minutes (one whistle). Don't cook after one whistle as overcooked arbi becomes sticky. [Tip: Soak arbi in some water to which salt is added for about 10 minutes. Since it's a root sometimes it is covered in mud, even if it's not it's better to soak it in water for some time.]
Soak cooked arbi in water (room temperature will do) to stop them from cooking further, and then cut them into approx. 1 inch slices.
Heat a kadai and add oil. (If you're using a non-stick kadai (which I would recommend) you will little more than 1 tbsp oil.)
Add cumin seeds when the oil heats up. [Tip: If you are making this sabzi for toddlers, you can use jeera powder instead of the seeds.]
Add hing and haldi when the cumin seeds splutter.
Add sliced arbi and give it a stir.
Add red chili powder and salt, and stir the sabzi so that the powder and salt get mixed properly. (I use less chili powder because I make it for Devansh. If you are making this sabzi for grownups you can add more chili powder as this sabzi tastes better when it's spicy.)
Cook without a lid till the sabzi turned slightly golden, add chopped coriander, give the sabzi a good stir, and then turn off heat. (Devansh still hates getting coriander in his bites so I add it after keeping some aside for him.)