In a large bowl, combine the squash, red bell peppers, sweet potato, and Yukon Gold potatoes. Separate the red onion quarters into pieces, and add them to the mixture.ary, olive oil, vinegar, salt, and pepper. Toss with vegetables until they are coated. Spread evenly on a large roasting pan.
Roast for 35 to 40 minutes in the preheated oven, stirring every 10 minutes, or until vegetables are cooked through and browned.