Preheat the oven to 425 degrees.
Trim both ends of the squash and cut the squash in half lengthwise. Scoop out the seeds and discard. Slice the squash crosswise into ½-inch-thick pieces.
Place the squash and onions on a sheet pan. Drizzle with the olive oil, sprinkle with the salt and pepper, and toss well. Spread out into one even layer.
Roast for 15 minutes. Add the walnuts to the sheet pan, toss, and roast for another 10 minutes, until the squash is tender and browned and the nuts are toasted.
While the squash roasts, make the balsamic glaze. Pour the vinegar into a small saucepan. Bring to a boil, then lower the heat and simmer, uncovered, for 8 to 10 minutes, swirling the pan occasionally, until the glaze is thickened and coats the back of a spoon. You should have 2 to 3 tablespoons of glaze. Remove from the heat and set aside.
Arrange the squash, onions, and walnuts on a flat serving dish. Pour the glaze evenly over the vegetables, then sprinkle with parsley and salt. Serve hot, warm, or at room temperature.Copyright 2019, Lidey Heuck, All Rights Reserved.