Gently boil the potatoes until just tender, drain well, arrange on a large baking sheet and cool to room temperature. Sprinkle with the carrot and green onion. (The potatoes can be prepared to this point a few hours in advance; cover and keep in the fridge until ready to serve.) Preheat the oven to 350 degrees F. Combine the lemon zest, lemon juice, mustard, sugar, salt, pepper and olive oil in a bowl; spoon over the potatoes. Bake 10 to 12 minutes, or until the potatoes are well heated through. Spoon into a decorative dish and serve.