Heat olive oil in a saucepan over medium-high heat, add onion, capsicum and garlic and fry, stirring occasionally, until translucent (4-5 minutes). Add minced beef and brown well, breaking up clumps with a wooden spoon (3-4 minutes), then stir in sugar and chilli. Add passata and stock, season to taste and simmer until thickened and well flavoured (8-10 minutes). Stir in vinegar and Worcestershire sauce, check seasoning.
Spoon meat into rolls, top with cheese, pickles and cos and serve with chips alongside.