To make the burgers, mix together all the ingredients and knead well so everything is thoroughly mixed. Separate the mix into 6, roll each into a large ball, then shape into burgers (see photos, right). Put them in the fridge and, if possible, leave to chill for at least 1 hr. They can be made up to 2 days ahead.
To cook the burgers, get the barbecue good and hot with the coals glowing. You don’t need to add any oil to the burgers. Put them on the barbecue and leave for a few mins until the edges start to colour, then slide a fish slice under the burgers and turn over. Repeat the process, then turn again. Remove to the cooler side of the barbecue and leave to cook for a good 15 mins if you like them well cooked.
While the burgers are cooking, BBQ the bacon and pineapple. Top the burgers with the bacon, then add the cheese and put back on the barbecue to melt. Warm the baps over the barbecue, too, if you like.
Divide the mayo between the bap bases and top with the burgers. Add the pineapple, beetroot, tomato and lettuce, then put the lids on top.