First cook the potato until 90% done in your preferred method (pressure cook, microwave, etc). Peel the skin and cut into cubes and keep aside. But make sure not to overcook.
Now heat a pan with oil, add the items listed under "To temper" in the given order. Once the urad dal turns golden brown, add the curry leaves, green chilli, onion, ginger garlic paste and saute until the onion turns translucent.
Now add the tomatoes, salt and saute until the tomatoes turns fully mushy.
Add the turmeric, sambar powder and mix well until combined. Add a cup of water, give a quick stir and cook in low-medium flame.
Once the mixture nicely boils and the oil starts to get separated over the top. Now add the potatoes, stir well and wait till the mixture get thickened up. By now all the raw smell of the powders will be gone and the masala will be absorbed by potatoes. Stir for a few more minutes until the masala is nicely roasted.
Turn off the flame and garnish with coriander leaves.
Serve hot as a side for sambar rice or any rice variety.