Dice potatoes into medium cubes.
Heat vegetable oil in a pan, sauté chopped onion, ginger paste, and garlic paste until golden.
Add chopped tomatoes, turmeric powder, red chili powder, and salt; cook until tomatoes break down.
Add cubed potatoes, green peas, and water; cover and simmer for 15 minutes until potatoes are soft.
Stir in garam masala and serve warm with rotis.