Meatball gravy sub - Good Food Middle East

Ingredients

• 1 tbsp olive oil
• 1 onion, ½ finely chopped, ½ sliced
• 1 garlic clove, crushed
• 250g pack beef mince
• ½ tbsp balsamic vinegar
• 100ml beef stock
• 1 tsp Worcestershire sauce
• 1 large ciabatta roll
• 2 slices mature cheddar
• mixed leaves, to serve (optional)