Preheat the oven to 180°C (160°C for fan assisted ovens)/Gas Mark 4. Lightly grease and line the base and sides of a 28cm x 18cm rectangular tin with baking parchment. Mix the brownie mix with the butter and eggs in a large bowl, until well blended.
Spread the mixture evenly into the lined tin. Bake in the centre of the oven for 18-20 minutes, or until a rounded knife, inserted 5cm from the edge of the tin comes out clean. Allow to cool for 30 minutes on a wire rack.
Place the tin of brownies into the freezer for 30 minutes. Remove the brownies from the tin, and peel away the parchment. Cut into 32 squares.
Line a baking sheet with foil. Thread 3 brownie squares, 2 pineapple chunks, 2 banana chunks and 2 strawberry halves alternately on each of 10 long wooden skewers (you will have 2 brownie squares left). Place on the baking sheet. Cover and chill in refrigerator whilst making the chocolate sauce.
Place the chocolate sauce ingredients into a heatproof bowl set over a saucepan of simmering water, and heat until the chocolate and butter have melted. Remove from heat, and stir until smooth. Drizzle over the skewers to serve.