Lightly toast the bread (the slices should be slightly crisp, but barely colored).
Steam the zucchini slices. They should remain fairly firm.
Spread the 4 slices of bread with a very thin layer of mustard. Place four slices of zucchini (in the corners), garlic and a chicken breast on the slices of bread. Spread generously with St. Agur Bleu.
Cover the sandwiches with the remaining slices of bread.
Brown on the grill. Do not allow to grill too long.