Melt the chocolate, butter and 1 teaspoon coconut oil in the top of a double boiler over simmering water, stirring frequently and scraping down the sides with a rubber spatula to avoid scorching. Remove from heat and stir in cinnamon.
Preheat oven to 180 C / Gas 4. Lightly grease a 2lb loaf tin with 1 teaspoon coconut oil.
Sift coconut flour, bicarbonate of soda and salt together in a bowl. Place mashed bananas in a large bowl; fold flour mixture into bananas with a rubber spatula.
Beat almond butter and eggs together in a bowl until creamy; add to banana mixture and mix well.
Pour 1/2 banana mixture into prepared loaf tin; top with 2 tablespoons of the chocolate mixture. Use a fork to spread and swirl the chocolate mixture through the banana cake mixture. Repeat with remaining banana cake mixture and chocolate mixture.
Bake in the preheated oven until top is golden brown and loaf cake is cooked through, 50 minutes.