Trim vegetables and cut lengthwise into 116-inch-thick ribbons with a U-shaped vegetable peeler.
Have ready a bowl of ice and cold water. Cook carrots in a large pot of boiling salted water 2 minutes. Add both squashes and cook until vegetables are crisp-tender, 1 to 2 minutes.
Drain vegetables and transfer to ice water, then drain in a colander.
Heat oil in a large skillet over moderate heat until hot but not smoking, then cook vegetables, tossing, until heated through. Season with salt and pepper.
