Heat the oil in a saucepan.
Add the cumin seeds and when they darken slightly, in about a minute, add the turmeric, green chilies, garam masala, and coriander powder.
Stir quickly for a few seconds, then add the peas and stir. If you did not have time to thaw first, stir-fry until they do and are tender.
Add the potatoes and lemon juice and salt to taste. Mix well.
Turn off heat.
Lay a sheet of filo pastry on a flat surface.
Brush on or spray oil evenly over the top. Layer on a second sheet. Continue until you've used up six sheets.
Place half the potato stuffing along the length of the filo pastry in a straight line, a couple of inches from the edge of the pastry.
Roll tightly, like you would a sushi roll. Pinch the ends together-- you don't have to get a perfect seal. Place seam side down on an oil-sprayed baking sheet. Spray on some more oil on the roll.
Repeat the process with the remaining pastry sheets and stuffing.
Bake in a preheated 350-degree F oven for 25 minutes or until the pastry has golden-brown spots.
Remove from the oven, let it cool until you can handle it, transfer to a chopping board, and with a serrated knife, slice into rounds.