Mix the melted butter, digestives and crushed pecans in a bowl until well combined. Press the mixture down into a 7½cm/3in diameter chefs' ring onto a plate. Chill.
Split the vanilla pod in half and use a knife to scrape out the seeds. Mix together the vanilla seeds, cream cheese, lime juice, sugar-substitute, to taste, yoghurt and half the berries in a mixing bowl.
Spoon the cream cheese mixture onto the cheesecake base. Top with the rest of the berries.
Gently remove the chefs' ring and serve.
