Preheat oven to 350°F. Spread walnuts on a baking sheet lined with parchment paper in a single layer. Bake for 5 minutes, toasting for 1 or 2 more minutes if needed but be sure not to burn. Remove from oven and let cool. In a medium saucepan, heat maple syrup until warm. Add the vanilla extract, salt and walnuts, quickly stirring and coating each piece with the syrup mixture. When walnuts are evenly coated, pour coconut flakes and fold to coat walnuts. Place nuts back on the parchment lined baking sheet using two forks to separate the walnuts from each other, working quickly to prevent walnuts from sticking excessively together. Cool completely before serving.