Line the bottom of an 8-inch (20 cm) springform pan with removable bottom with parchment paper. Press the oat bars into the pan to completely cover the bottom in an even layer. Set aside.
In a bowl, beat the cream cheese, icing sugar, lemon juice and vanilla with an electric mixer. Add the 35% cream and whisk until stiff peaks form. Pour half of the cheesecake mixture over the oat bar crust. Top with the blueberries and raspberries. Cover with the remaining cheesecake mixture. Smooth out the surface of the cake using a small offset spatula. Cover and refrigerate for 5 hours or until the cheesecake mixture is set.
Run a thin blade between the cake and the side of the pan. Gently unmould. Garnish with more blueberries and raspberries, if desired. The cheesecake will keep for 4 days in the refrigerator.