Boil the potatoes and peel. Dice into 1/4 inch pieces. In a frying pan, put the cumin and coriander seeds. Toss for about 30 seconds and remove seeds. Grind into powder. Heat 4 tablespoons of oil in a frying pan and sauté the onion until light brown. Add the peas, ginger, green chili, chili powder, fresh coriander, salt, pepper and 3 tablespoons of water. Cover and simmer until peas are tender, about 5 minutes.
Add more water if necessary. Add the diced potatoes, roasted and ground coriander and cumin seeds, lemon juice, all spice and stir fry for 3-5 minutes. Allow stuffing to cool before filling the samosas or rolls.