Whisk the yogurt, add the orange marmalade and mix well. The mixture will be smooth.
Whip the heavy cream in a bowl by using an electric mixture or a whisk until peaks form.
Add powdered sugar to the orange zest and let it rest for 5 minutes. Add the zest to the yogurt mixture and mix well.
Boil the orange juice and reduce it by half. Add agar agar powder to the juice and mix, simmer for 5 minutes for the agar agar powder to completely dissolve in the juice. Let the mixture cool down but make sure it doesn’t start to solidify.
Add the agar agar powder-orange juice mixture to the yogurt mixture and mix well.
Lightly fold in the yogurt mixture into the whipped cream with a spatula.
Pour the mousse mixture over the cooled ginger snaps layer and place it in refrigerator for at least 4 hours.