To make sauce, combine all ingredients in a jug. Season with salt and pepper. Mix well and set aside

Preheat grill to high heat

Divide Mozzarella into four even amounts. Set aside

To make patties, combine mince, onion, egg yolk, breadcrumbs and mustard in a large bowl. Season with salt and pepper. Mix well. Divide mixture into four equal portions. Shape portions into patties, about 10 cm in diameter (5 mm thick)

Heat oil in a large non-stick frying pan over medium-high heat. Add the patties. Cook for about 6 to 7 minutes on each side, or until browned. Top the centre of the patties with Mozzarella. Cover pan with lid. Cook for a further 3 to 4 minutes, or until cheese has melted. Remove patties from pan

Meanwhile, split rolls in half horizontally. Place cut-side up on an oven tray. Grill for 2 minutes, or until lightly toasted. Remove

To assemble, spread each bun base and top with 1 tbsp. of the sauce. Top bases with lettuce, tomato, patties and jalapenos. Replace bun tops. Serve with remaining sauce