Rinse the arbi thoroughly under running water to remove any dirt or debris. Then, place them in a pressure cooker with enough water to cover the roots. Cook for 2-3 whistles, or until they are just tender but not mushy. Allow the pressure to release naturally before opening the cooker.

Drain the arbi and let them cool. Once cool, gently peel off the skin and cut each root into 1-inch thick round slices.

In a large pan or kadhai, heat the vegetable oil over medium heat. Add the cumin seeds and asafoetida, and let them sizzle for a few seconds.

Stir in the ginger-garlic paste and cook for another 2 minutes, or until the raw smell dissipates.

Add the chopped tomatoes, turmeric powder, red chili powder, coriander powder, and salt. Cook the mixture for about 8-10 minutes, or until the tomatoes are soft and the oil starts to separate from the masala.

Gently mix in the boiled and sliced arbi, ensuring that each piece is well-coated with the masala. Cover the pan and let the arbi cook in the spices for 5-7 minutes, stirring occasionally.

Sprinkle garam masala powder over the sabji, and give it a gentle stir to combine. Cook for an additional 2 minutes, and then turn off the heat.

Garnish the Arbi Sabji with chopped coriander leaves before serving.