In a Dutch oven or large sauté pan over medium-high heat, lightly brown the cauliflower and onion in the butter. Add the vinegar and sugar. Continue cooking for about 2 minutes. Add the remaining vegetables and the cashew mixture. Stir to coat the vegetables. Add the remaining ingredients. Cover, reduce the heat and simmer gently, stirring frequently, until the vegetables are tender, about 20 minutes. Season with salt and pepper.