How to Make It
In a large saucepan of boiling water, cook the potatoes until tender, about 20 minutes. Drain and cool slightly. Peel and slice 1/4 inch thick.
Meanwhile, in a large skillet, heat 3 tablespoons of the olive oil. Add the red onion and scallions and cook over moderate heat, stirring occasionally, until softened and golden, about 10 minutes.
In a small bowl, whisk the remaining 3 tablespoons of olive oil with the mustard and lemon juice. Add the dressing to the skillet along with the potatoes, pickles and snap peas and season with salt and pepper. Cook over moderately low heat, tossing, until just warmed through, then serve.