Add fiber syrup, water, lemon juice and zest to a small pot and let it get warm on low heat. Stir regularly. Taste to check if more fiber syrup, water or lemon juice is needed depending on how you prefer your syrup.
Meanwhile peel, deseed and cut all the fruits and place in a deep bowl.
Pour the warm syrup into a small bowl.
Drizzle the syrup over the fruit salad, top with hazelnuts and mint.