In a large pan, combine dried fruit, zests and juice, rum, coconut oil, and sugar. Heat, stir, and simmer for 5 minutes. Transfer to a bowl and cool for 30 minutes.
Preheat oven to 150°C (130°C fan/gas 2). Line a 20cm cake tin with double parchment, wrap in newspaper, and secure with string.
Mix chia seeds with 150ml water and let sit for 5 minutes until thick.
Add remaining ingredients and chia mix to the fruit mixture. Stir well, checking for flour pockets.
Pour mixture into the tin, level, and bake for 2 hours.
Remove from oven, poke holes with a skewer, and spoon over 2 tbsp rum. Cool completely in the tin.
Peel off parchment, wrap in cling film, and store. Feed with 1-2 tbsp alcohol every two weeks, stopping a week before icing.