Slice the potatoes into long wedges. Sprinkle with olive oil and season with pepper and salt. Arrange them on a layer of parchment paper on a baking sheet and bake for 30 minutes in an oven preheated to 220°C/425°F.
Slice open the hamburger buns. Cook the chicken burgers.
Spread a layer of guacamole on the bottom half of the hamburger bun and place the chicken burger on top. Top the burger with the Manna truffle mayonnaise and garnish with watercress. Finish with the top half of the hamburger bun.
Serve the hamburgers, together with the potato wedges.