Combine the crushed chocolate cookies or brownie crumbs with melted butter in a bowl. Press mixture into the bottom of a 9-inch springform pan. Refrigerate for 30 minutes.

Whip the heavy cream in a bowl until soft peaks form. Blend the cream cheese (or Greek yogurt), sugar, and melted dark chocolate until smooth. Fold the whipped cream into the chocolate mixture. Spread the mousse over the crust and refrigerate for 2-3 hours.

In a saucepan, whisk orange juice, honey, and cornstarch over medium heat until thickened, about 4-5 minutes. Pour over the set mousse layer and cool slightly.

Run a knife around the edges of the pan, release dessert, and transfer to a serving plate. Garnish with fresh orange slices or zest. Serve chilled.