Place the onion rings and the buttermilk into a shallow container, mix well and leave to soak for up to 12 hours but 4 hours will do,
Pre-heat the oven to 200 degrees then measure the flours, salt & pepper into a bowl and dip the onion rings into it coating each piece with some of the mixture. Place them onto a lined baking tray and spray with olive oil spray,
Bake in the oven for 30 minutes turning the onions over half way through cooking and spray with a little more oil,
After 30 minutes remove from the oven, sprinkle with the smoked paprika and eat with the burger.
Scoop the avocado flesh into a bowl, season well, add in the lemon juice and the chilli (if using) then set aside.
For the candied bacon:)
Pre-heat the oven to 170 degrees,
Measure the maple syrup, brown sugar and mustard into a bowl then add in the bacon and coat each piece in the sauce,
Transfer the bacon to a lined baking tray then bake in the oven for 25 minutes until it is beginning to brown around the edges then set aside.
Heat 2tbsp oil in a saucepan and brown the burgers briefly on each side before transferring to the oven (in the pan) to finish off cooking for 15 minutes,
Remove from the oven and place the burgers in the brioche buns, to with smashed avocado and candied bacon. Serve with the onion rings and sauces of your choice.
You could soak the onions and marinade the bacon the day before but prepare the smashed avocado at the last minute or it will discolour - even with the added lemon juice.
There will be leftover candied bacon which you can enjoy over the next day or two. It is also good with eggs or in salad or as part of a sandwich filling.