For the ladyfingers: Preheat the oven to 350 degrees F. Line a rimmed baking sheet with parchment paper and dust lightly with confectioners' sugar.
Sift together the flour, cocoa powder and salt in a bowl.
Put the egg whites in a large bowl and beat with an electric mixer on medium-high speed until frothy. Gradually add 1/2 cup of the granulated sugar and beat until stiff, shiny peaks form, about 6 minutes.
In a medium bowl, beat the yolks and remaining 1/4 cup granulated sugar until pale and thick. Beat in the vanilla. Gently fold the yolks into the egg whites; it's okay if some streaks remain. Add the flour mixture and fold gently, but thoroughly, until well mixed.
Spoon the mixture into a piping bag fitted with a 3/4-inch plain tip. Pipe 3-inch-long, 1-inch-wide ladyfingers about 1/2 inch apart. Dust the tops of the cookies lightly with confectioners' sugar. Bake until springy to the touch, 16 to 18 minutes. Cool completely.
For the decoration: Combine the chocolate and coconut oil in a small microwave-safe bowl. Microwave, stirring every 30 seconds, until melted. Dip one end of each ladyfinger in the chocolate, then sprinkle with the coconut over parchment paper. Place on a serving platter.
Refrigerate until set. Serve immediately or keep refrigerated until ready to serve, up to 4 hours (ladyfingers dry out quickly).