Preheat oven to 425.
Spray a large baking sheet with cooking spray, or lightly coat with oil. Add peppers, onions, and cauliflower to pan.
Drizzle with oil and vinegar; toss to coat. Roast 15 mins or until veggies are softened and slightly browned.
Remove pan from oven, push veggies to one side to allow room for sausage. Place sliced sausage on pan and return to oven.
Cook for another 10 mins or until sausage is browned and heated through.
Remove from oven and top with chopped parsley, if using. Season with salt and pepper to taste.