Boil, peel, and mash potatoes lightly.
Heat oil in a pan, add mustard seeds, curry leaves, chopped green chili, and sliced onion; sauté until translucent.
Add turmeric powder, salt, and mashed potatoes; mix well with 2 tbsp water and cook for 3 minutes.
Heat a skillet, pour a ladle of dosa batter, and spread thinly in circles.
Drizzle oil around edges, place potato mixture in center, fold when crisp, and serve hot.