In a mixing bowl, combine the ground chicken, boiled and mashed potatoes, finely chopped onion, minced garlic, grated ginger, cumin powder, coriander powder, garam masala, chili powder, salt, chopped cilantro, and lemon juice. Mix well until all ingredients are evenly incorporated.
Take a samosa pastry sheet and lay it flat on a clean surface. Cut it into two halves to form two rectangles.
Take one rectangle and fold it into a cone shape, sealing the edge with a bit of water. Allow the bottom of the cone to be open for filling.
Fill the cone with a spoonful of the chicken filling, making sure not to overfill.
Seal the open end of the cone by pressing the edges together, ensuring there are no gaps. Use a little water if necessary to help seal it properly.
Repeat the process with the remaining pastry sheets and filling.
Heat oil in a frying pan or deep fryer over medium heat.
Once the oil is hot, carefully add a few samosas at a time to avoid overcrowding. Fry until they turn golden brown and crispy, about 5-7 minutes.
Use a slotted spoon to remove the samosas and drain them on paper towels.
Serve hot with mint chutney or tamarind sauce for dipping.