Boil potatoes, then peel when cool and cut into chunks add into a small heavy skillet and heat in oil. Add cumin seed and stir a few seconds, until you can smell the spice. Be careful to avoid burning, this should take about 15 seconds. Add Onion and sauté on low heat until translucent. Add remaining spices and stir for a few seconds. Add Potato chunks and toss to coat with spices and onions. Keep tossing until Potato is hot. Add lemon juice and serve immediately.