In a bowl, combine the semolina, chickpea flour, whole wheat flour, and yogurt. Add 1/2 teaspoon salt and enough water to make a batter. Mix well, cover, and let it rest for 30 minutes. Heat a griddle or skillet and brush with oil. Pour a little batter and spread it to form a dosa. Drizzle some oil around the edges and cook until golden and crispy. Your crispy sooji dosa is ready.

To prepare the filling, heat oil in a pan. Add mustard seeds, split chickpeas, and curry leaves. Add the sliced onion, ginger, and green chilies, and sauté. Add salt, turmeric, and red chili powder. Add the finely chopped boiled potatoes and mix well.

Cover and cook for 2-3 minutes. Add the chopped cilantro and mix. The potato filling is ready. Serve inside the dosa.