Thinly slice the orange peel and flesh, removing any seeds.

Simmer the sliced orange with the water, lemon juice and sugar over low heat for 12 minutes, until the peel softens.

Before removing from the heat, stir in the chia seeds and simmer for another 3 minutes; it will thicken further as it cools.

Pour the hot marmalade into a clean, dry jar and seal the lid tightly.