Preheat oven to 375F. Spray a baking dish with oil & spread potatoes in a single layer. Spray potatoes with oil & sprinkle with paprika. Bake until pale gold & just cooked, 35 to 40 minutes. Scrape into a mixing bowl; fold in carrots & parsley.
Preheat a pan over moderately high heat. Add mustard seeds, cover & cook until they begin to splutter. Add cumin seeds & cook gently for a few seconds. Remove pan from heat & add olive oil, stock & juice, whisk to mix. Pour over vegetables, season & toss to mix. Garnisnh with pistachios.