Heat oil in a non-stick pan and saute cumin seeds till they start to sizzle. Add in onions and garlic, and fry till lightly brown.
Stir in spices and salt, and saute for a few seconds before adding in the tomatoes. Mix well.
Once the tomatoes start to soften, add in the cubed potatoes and mix to combine well with the spices. Let it cook for 3-4 minutes, stirring occasionally in between.
Garnish with chopped green onion and serve warm.