Preheat oven to 180°C (356°F).
In a large mixing bowl, place two peeled bananas and mash them using a fork.
Add walnuts in a food processor and process until nuts are fine and evenly ground. Don't process too long or they will become oily.
Add ground walnuts, coconut sugar, baking soda, baking powder, cardamom, water, and all-purpose flour to a mixing bowl and stir until combined.
Line the bottom of a loaf pan with parchment paper.
Pour the batter in the pan, top with chopped walnuts and lingonberries, and bake for 35-40 minutes.
Test the bread with a toothpick. It should come out clean.
Let cool completely before slicing.