Put the oil in a medium, preferably nonstick pan, and set over medium heat.
When hot, add the cumin seeds.
Let them sizzle for 10 seconds before adding the chopped onions.
Stir and fry the onions for 5–6 minutes, or until they have softened and turned translucent.
Add the grated ginger, green chilies, and turmeric.
Stir continuously for one minute until fragrant.
Add the peas, diced potatoes, salt, and pepper.
Stir everything together for 2–3 minutes to heat through. If the mixture looks too dry, sprinkle with a tablespoon of water to create a little steam.
Serve hot.