Preheat your oven to 350°F. Grease a 9-inch round cake pan and line the bottom with parchment paper. In a medium bowl, combine the gluten-free chocolate cookie crumbs, melted butter, and granulated sugar. Mix until well combined and press into the bottom of the prepared cake pan. Bake for 10 minutes and let cool completely.
Melt the semi-sweet chocolate chips in a microwave-safe bowl in 30-second intervals, stirring until smooth. Allow to cool slightly. In a large mixing bowl, whip the heavy cream until soft peaks form. Gradually add powdered sugar, vanilla extract, instant coffee granules, and salt. Continue whipping until stiff peaks form. Gently fold the melted chocolate into the whipped cream until fully combined.
Pour the chocolate mousse over the cooled crust in the cake pan and smooth the top with a spatula. Chill in the refrigerator for at least 4 hours until set.
Once set, carefully remove the cake from the pan and peel off the parchment paper. Slice and serve.