Cut the avocados in half and remove the stone. Using a dessert spoon, scoop the flesh from the skin, in one piece, and discard the skin. Put the halves cut-side down on a chopping board and cut thin slices through the avo, lengthways (from top to bottom), keeping the shape of the avocado. Push the top pieces to the right, and the bottom pieces to the left on the chopping board, but make sure the slices are still overlapping slightly, so you make a thin strip of overlapping avocado slices. Starting from one end, curl the pieces into a spiral, tucking in any pieces that fall out. It should end up looking like a flower. Squeeze over a little lemon juice and a pinch of chilli flakes.