Soak the chia seeds in the given water for 10 minutes.
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Next, add the dates to another bowl, cover with water, and leave them to soften for 10 min. Then, drain them.
In a food processor, blitz the dates with zucchini into a smooth purée.
Now, combine the zucchini purée with cocoa, chia-egg, peanut butter, baking powder, vanilla, and melted chocolate.
Transfer the dough into a 20 cm (8 inches) square baking tin, level it with a spatula, and sprinkle it with chopped cashew nuts.
Bake the brownie slab for 35 minutes at 200°C (390°F), and leave it to cool down completely before slicing into squares.