Step 1: Place mince, onion and sauce in a large bowl. Season with salt and pepper. Using clean hands, mix until well combined. Divide evenly into 8 portions. Roll each portion into a ball. Working with 1 ball at a time, flatten between the palm of your hands and then on a flat surface to a 9cm-diameter patty. Transfer to a large baking paper-lined tray. Refrigerate for 20 minutes.
Step 2: Meanwhile, combine dijonnaise, yoghurt and dill in a small bowl. Season with salt and pepper. Preheat grill on medium. Using a serrated bread knife, cut each bread roll horizontally into 3 slices. Place slices on a tray. Grill cut sides of rolls for 1 to 2 minutes or until golden.
Step 3: Place flour on a large plate. Press patties into flour to lightly coat. Spray a large non-stick frying pan with oil. Heat over medium-high heat. Add half the patties. Cook, turning carefully, for 2 to 3 minutes each side or until cooked through. Transfer to a plate. Cover with foil to keep warm. Repeat with remaining patties.
Step 4: Place bases on plates. Spread with one-third of the yoghurt mixture. Top with half the lettuce, the cheese and half the patties. Repeat with remaining ingredients, finishing with a layer of sauce, then roll top. Serve.
