Add the raspberries, granulated sugar, and lemon juice to a small saucepan.

Whisk the cornstarch and water together until completely smooth and free of lumps. Pour the mixture into the saucepan.

Bring the raspberry mixture to a boil, then reduce the heat and simmer for about 5 minutes, stirring frequently. Gently mash the berries against the side of the saucepan with the back of a spoon.

Set a fine-mesh strainer over a bowl. Pour in the raspberry mixture and press it through the strainer with a spoon to create a smooth raspberry sauce for cheesecake. Let it cool to room temperature, then refrigerate until completely chilled.

Combine the graham cracker crumbs and melted butter in a medium bowl. Stir until all the crumbs are evenly moistened. Set aside.

Using an electric mixer fitted with a whisk attachment, beat the cold heavy cream until soft peaks begin to form. Gradually add 1/3 cup powdered sugar and continue beating until stiff peaks form.

Transfer 1/2 cup of the whipped cream to a piping bag for decorating. Place the remaining whipped cream in a separate bowl and refrigerate.

Beat the cold cream cheese until smooth. Add the remaining 1 cup powdered sugar, lemon zest, and vanilla extract. Beat until smooth and thoroughly combined, scraping down the sides of the bowl as necessary.

Gently fold the reserved whipped cream into the cream cheese mixture. Avoid overmixing so the mousse stays light and airy.

To assemble the No-Bake Cheesecake with Raspberry Sauce, spoon 2–3 tablespoons of graham cracker crumbs into each serving cup. Add about 2 tablespoons of chilled raspberry sauce, followed by a generous layer of cheesecake mousse.

Finish with piped whipped cream and garnish with fresh raspberries and mint leaves, if desired. Refrigerate until ready to serve.