Preheat the oven to 350°F. Spread the walnuts on a baking sheet lined with parchment paper or a silicone liner in a single layer then bake for 5 minutes, toasting for 1 or 2 more minutes if needed but be sure not to burn. Remove them from the oven and let them cool.
In a medium saucepan, heat the maple syrup until it's warm. Add the vanilla extract, salt and toasted walnuts, quickly stirring and coating each piece with the syrup mixture. When walnuts are evenly coated, pour in the coconut flakes and fold them gently to coat the walnuts.
Place the walnuts back on the parchment lined baking sheet using two forks to separate them from each other, working quickly to prevent walnuts from sticking excessively together. Cool completely before serving, about 20 minutes.