Preheat your oven to 325 degrees F. Line a baking sheet with parchment paper.

Shred the zucchini on the fine side of a box grater. This is the most important step: wrap the shredded zucchini in a clean kitchen towel and squeeze firmly over the sink until no more liquid comes out. Then squeeze again. Wet zucchini will make the macaroons spread flat and they will not set up properly. You should have about 3/4 cup of very dry shredded zucchini after squeezing.

In a large mixing bowl, combine the dry zucchini, sweetened shredded coconut, egg whites, granulated sugar, vanilla, and salt. Stir everything together until well mixed and the coconut is evenly coated with the egg whites.

Using a cookie scoop or a heaping tablespoon, scoop mounds of the mixture onto the prepared baking sheet about 1 1/2 inches apart. Press each mound gently with your fingers to compact it slightly so it holds its shape. Loose piles will fall apart.

Bake for 18 to 20 minutes until the tops and edges are golden brown. The coconut should look toasted and the bottoms should be a deep golden color. Do not pull them early. Under-baked macaroons will be soggy rather than chewy.

Transfer the macaroons to a wire rack and let them cool completely. They need to be fully cool before dipping in chocolate or the chocolate will melt off.

When the macaroons are cool, melt the dark chocolate in a small microwave-safe bowl in 30-second intervals, stirring between each, until smooth. This usually takes about 90 seconds total.

Dip the flat bottom of each macaroon into the melted chocolate, letting the excess drip back into the bowl. Set them chocolate-side up on the parchment-lined baking sheet. Let the chocolate set at room temperature for about 20 minutes, or place the tray in the refrigerator for 10 minutes to speed things along.