In a double boiler, whisk egg whites, sugar and salt together. Heat, stirring constantly until the sugar is dissolved and the mixture is thoroughly heated, then remove from heat.
Stir in vanilla extract and lemon zest.
Add shredded coconut and flour, stir until combined.
Cover the bowl with plastic wrap and refrigerate for 45 minutes.
Preheat oven to 325°F (160°C) and line a large baking sheet with parchment paper.
Using two spoons, drop heaping tablespoons of the mixture on the prepared baking sheets, spacing about 1 inch apart.
Bake for about 20 minutes until the tops and edges are golden.
Let cool on the baking sheet for 10 minutes, then transfer to a cooling rack to cool completely.
When the macaroons are cooled completely, melt the chocolate in a double boiler over simmering water (or in the microwave).
Dip the bottoms of the macaroons in the melted chocolate. Let any excess drip back into the bowl and put the macaroon back on the baking sheet lined with a silicone baking mat or parchment paper. Drizzle tops with chocolate if desired. Let stand until set.
Then store in an airtight container at room temperature.