Make the red onion pickle: Boil some water in a kettle. Mix vinegar, sugar and salt in a over-proof bowl. Pour a small amount of boiled water until all dissolve. Add in the sliced onions and let sit for 1 hour.
In medium-high heat pan, add a spray of canola oil. Roll beef mince and squish into a ball about the size of a handball. Season well with salt and pepper. When the pan is hot place it on the pan, and then with the back of the flipper - squish down into patties. Season more with salt and pepper. Leave for 2-4 minutes and then flip. Repeat until done.
Cut buns in half and spread inside of bun with butter/marg. Broil under the oven for 3 mins till crispy on top.
Homemade Aoili: Mix mayo, minced garlic and lemon juice together till well combined.
Spread buns with aoili. Add beetroot slices, add patty, add cheese, add avocado and then finish with the pickled onions.
I use 2 star beef mince from Aldi ($3.39) and it works wonders! The measurements may be a bit chopped - but just go with your guts!!