In a mixing bowl, combine the flour and salt. Add the vegetable oil and mix until the mixture resembles coarse crumbs. Gradually add the water and knead the dough until it is smooth and pliable. Cover the dough with a damp cloth and let it rest for 30 minutes.
In a large skillet, heat 2 tbsp. of oil over medium-high heat. Add the chopped onion and sauté until it is softened. Add the ginger and cook for another minute.
Add the mashed potatoes, green peas, chopped cilantro, ground cumin, ground coriander, garam masala, salt, and black pepper to the skillet. Stir everything together and cook for 5-10 minutes, until the mixture is heated through.
Divide the dough into 8 equal portions. Roll each portion into a circle, about 6 inches in diameter.
Cut each circle in half to form two semicircles. Brush the straight edge of each semicircle with water.
Take one semicircle and fold it into a cone shape, overlapping the straight edge slightly. Seal the edge by pressing it together. Fill the cone with the potato and pea mixture, leaving a little bit of space at the top.
Brush the top edge of the cone with water and press it together to seal the samosa.
Heat oil in a frying pan or preheat the oven to 375°F to bake the samosas. Fry or bake the samosas until they are golden brown and crispy.
Serve the samosas hot with chutney or ketchup on the side.
Notes
Note: Samosas can be stored in the fridge for up to 3 days, or frozen for up to 1 month. To reheat, place the samosas in a 375°F oven for 10-15 minutes, or until heated through.