Preheat the griller to high. Cut the meat into 20 equal cubes. Peel, top and tail the red onions, cut in half widthways and cut each half into four wedges. Trim the spring onions to 4-cm lengths and cut in half lengthways.
Thread five pieces of meat onto each of four metal skewers, about 38cm long, alternating the meat with a combination of red and spring onions.
Place the skewers across the griller tray or a small baking dish, balancing their ends on the rim.
Mix the mustard, Worcestershire sauce, vinegar, salt and pepper in a small bowl, then whisk in the oil.
Brush half the mixture over the top of the kebabs, then grill, close to the heat source, for 3–5 minutes. Turn the skewers, brush with the remaining mixture and grill for a further 3–5 minutes. If the kebabs start to burn, lower the griller tray a little.
The kebabs can be served on their own, but taste even better with a sauce made from the pan juices. Put the kebabs in the oven to keep warm. Pour the wine into the griller tray and stir over moderate heat, scraping up any sediment. Cook until the sauce is reduced by half, then season to taste and pour over the kebabs.
These kebabs are ideal for a quick and easy barbecue as well.