Place dark chocolate chips in a microwave-safe bowl and heat in 30-second intervals, stirring until melted and smooth. Alternatively, melt using a double boiler. Set aside to cool slightly.
Pour heavy cream into a chilled mixing bowl. Whip with an electric mixer or hand whisk until soft peaks form. Reserve about 1/4 cup for topping.
In a separate bowl, combine pumpkin puree, sugar, vanilla extract, pumpkin pie spice, and salt. Stir until smooth and fragrant.
Slowly fold the spiced pumpkin mixture into the melted chocolate, combining gently to avoid deflating.
Carefully fold the whipped cream into the chocolate-pumpkin mixture in batches, using a gentle folding motion to keep the mousse light and airy.
Layer crushed graham crackers in the bottom of serving glasses, then add a generous layer of chocolate pumpkin mousse. Repeat layers, ending with mousse on top.
Top each parfait with reserved whipped cream and garnish with chocolate shavings and additional crushed graham crackers if desired.
Refrigerate parfaits for at least 2 hours to set and meld flavors. Serve chilled.