Place the mince in a bowl, season well then work the meat together with your hands until it becomes sticky. Incorporate the mustard and chives, then carefully work in the cubes of cheese.
Shape the mix into 4 patties, about 9cm across, and make a small indentation in the middle of each to stop them turning into balls as they cook.
Place on a plate, cover and chill for at least 30 minutes.
Rub the burgers with the oil and cook on a hot barbecue or griddle for 4-5 minutes each side or until cooked through and no pink meat remains. Set aside to rest.
Meanwhile, cook the bacon until crisp and toast the cut sides of the rolls on the griddle or barbecue.
To serve, top each base with a burger, ketchup, gherkin, tomato, bacon, lettuce. Finish with the top of the roll and secure with a skewer if necessary.