Whisk melted butter, eggs, brown sugar and vanilla into a bowl. Pour the banana mix into this and whisk throughly. Next sieve flour, baking soda and salt into this mix and stir until combined. Gently fold in the roasted walnuts (roasting the walnuts gives it a nice crunch). Coating the chocolate chips with 1/2 teaspoon of flour ensures that the chocolate chips don't sink to the bottom of the pan, and spread evenly in the banana bread. Fold the dusted chocolate chips into batter.