1. In a mixing bowl, combine flour, salt, and oil. Gradually add water and knead into a smooth dough. Cover and set aside for 20 minutes.
2. Heat oil in a pan, add cumin seeds, and let them splutter. Add mashed potatoes, green peas, turmeric, garam masala, and salt. Mix well and cook for 5 minutes. Add coriander leaves and mix. Let it cool.
3. Divide the dough into small balls. Roll each ball into a thin circle. Cut the circle in half to form two semi-circles.
4. Take one semi-circle, fold it into a cone shape, and seal the edge with water. Fill the cone with the potato mixture and seal the top edge.
5. Heat oil in a frying pan. Deep fry the samosas until golden brown. Drain on paper towels.