Though it is not necessary, I do prefer to form this salad in a cylindrical mould.
Begin by placing some of the potato in the bottom of the mold and compacting.
Add to this a squeeze of the aioli, on top of which you place some of the tomato.
Next add some of the beans, followed by more aioli, then some egg.
Next add a piece of tuna, and compact down firmly.
Finish with more aioli, and an arrangement of lettuce on top.