Preheat the oven to 175°C (350°F) with a rack in the centre. Line a 20 cm (8 inch) square tin with parchment, leaving overhang on two sides.
Rinse the chickpeas well and pat them dry.
Blend the chickpeas, peanut butter, maple syrup, protein powder, baking powder, vanilla and salt in a food processor for 2 minutes, scraping down, until completely smooth.
Fold in the chopped chocolate and spread the batter evenly in the tin.
Bake for 20 to 22 minutes, until golden at the edges and a toothpick in the centre comes out with a few moist crumbs.
Cool completely in the tin, at least 1 hour, before lifting out and cutting into 12 squares.