Preheat the oven to 180 C (350 F). Lightly grease a 20-cm square cake tin, and line the base with baking (parchment) paper, extending over two opposites.
Combine all the ingredients except the pecans in a food processor. Process until smooth and well combined.
Spoon the mixture into the prepared tin and smooth the surface. Sprinkle the pecans over the top and gently press into the mixture.
Bake for 25 minutes, until the brownie is firm to a gentle touch in the centre. Leave in the tin for 5 minutes, then lift out onto a wire rack and slide the paper out. Leave to cool completely, then cut into 16 squares.
Brownies will keep for up to a week in an airtight container. Replace the canned black beans with 1-1/2 cups cooked beans made from 1/2 cup dried beans, if desired.
Each serving (1 brownie) provides: 690 kJ 165 kcal 4 g protein 12 g fat (3 g saturated fat) 13 g carbohydrate (7 g sugars) 3 g fibre 68 mg sodium