Place the potatoes in a saucepan, cover with water by an inch, bring to a boil, cover and let the potatoes cook 10 minutes or until a knife pierced in the center of a potato goes through cleanly. Remove the potatoes from the heat, drain, and reserve.
Preheat the oven to 350 degrees.
On a baking sheet lined with parchment or coated with cooking spray, place the potatoes an inch apart. Using your fingers or the heel of your hand or a fork, smash each potato, using just enough force so the potato flattens but holds together in a single piece.
Place the potatoes in the oven and bake for 45 minutes, turning the potatoes over once halfway. After the potatoes have cooked, remove them to a bowl.
In a small skillet, heat the oil. Add the mustard seeds and, when they sputter, add the jalapeno, curry leaves and turmeric. Stir-fry for a minute or two until the curry leaves become crispy.
Turn off the heat, and pour the seasoned oil and all of the seasonings over the potatoes, then add the lemon juice. Use salad spoons or two ladles to toss the potatoes with the dressing.
Serve immediately or at room temperature.