Mix the vinegar, oil, honey and garlic, season.
Place the onion on a grill tray, mix with 4 tbsp of gravy, coat the sausages with a little of the gravy. Mix the remainder of the gravy with the rosemary and set aside.
With the lid down, grill the onions over/on a medium heat (approx. 200 °C for approx. 15 mins., stirring occasionally. Add the sausages, continue to grill for approx. 10 mins. until cooked. Mix the onions with the reserved gravy, serve with the sausages.