Line a baking sheet with baking parchment. Melt the dark chocolate, either in a bowl over a pan of gently simmering water, or in short bursts in the microwave; don't let the chocolate get too hot.
Melt the white chocolate in the same way then pour half of it into a separate bowl. Stir the matcha powder into one half and the blueberry powder into the other. If the chocolate becomes too thick, give it a couple of seconds in the microwave to re-melt it.
Pour the dark chocolate onto the prepared baking sheet and use the back of a spoon to spread it out into a rough rectangle. Drizzle both white chocolates over the top, reserving a little bit of each.
Scatter over the goji berries, almonds, pumpkin seeds, bee pollen and chia seeds then drizzle over the remaining white chocolate. Set aside for a couple of hours at room temperature, or 20 minutes in the fridge until the chocolate has set then use a sharp knife to chop the slab into rough pieces. Store in an airtight container.