Sauté your cumin seeds in oil first and then add in your hing.
Next, add in your red onions and cook until translucent.
Then, add in your ginger and garlic and sauté for another 30 seconds before adding in all of your spices (except for the salt)
Cook the spices for about a minute. Make sure to keep the heat on low or low-medium so the spices don't burn.
Add in your crushed tomatoes, salt, and green chillies and cook for a few minutes until the oil starts to separate from the mixture.
Peel and chop your potatoes and add them in as well along with about a cup of water.
Let everything boil until the potatoes are cooked all the way through. You can also adjust the consistency as you like. You can serve this dish "dry" = "sookay." Or, you can add extra water and make it a curry.