Grill your brioche bun golden brown in a pre-heated oven.
Marinate your burger with the Worcester sauce and grill it in the olive oil.
Cut the red onion in rings and marinate them in the sushi vinegar.
Cut the brioche bun in half, horizontally of course.
Assemble your burger:
Mayonnaise on the bottom, some little gem, the burger, slices of tomato, some watercress, few more drops of mayonnaise and the top half of the brioche bun.
Serve with baked potato wedges and the rest of the mayonnaise.