Melt 8 oz of the sugar-free dark chocolate with the coconut oil in a heatproof bowl over simmering water, stirring until smooth. Let it cool for 2 minutes.
Using a pastry brush or the back of a spoon, coat the inside of 12 silicone muffin cups with a thick, even layer of melted chocolate, making sure to bring it all the way up the sides. Use about two-thirds of the melted chocolate and reserve the rest.
Freeze for 10 minutes until the chocolate is set, then apply a second coat with the remaining chocolate for extra thickness. Freeze again for 15 minutes. In a bowl, whip the heavy cream to stiff peaks. In a separate bowl, beat the mascarpone cheese, powdered erythritol, and vanilla extract until smooth.
Gently fold the whipped cream into the mascarpone mixture until light and fluffy. Fold in the diced strawberries carefully.
Carefully peel the silicone molds away from the chocolate cups. Fill each chocolate cup with the strawberry mascarpone cream.
Top each cup with a fresh strawberry half and drizzle with melted sugar-free dark chocolate in a zigzag pattern.
Refrigerate for at least 30 minutes before serving. The combination of the crisp chocolate shell, creamy mascarpone filling, and fresh strawberries is absolutely stunning.
