Mix together the yogurt and 2 tablespoons honey in a bowl until blended. Stir together 1/4 cup water, the sugar, remaining honey, zest, cinnamon, star anise and vanilla bean in a saucepan over medium heat. Add the plums and peaches and cook until saucy and tender, 8 to 10 minutes. Remove from the heat and chill until cold. Layer the stewed fruits and yoghurt in a tall glass. Finish with a dollop of yoghurt, garnish with walnuts and drizzle with honey.