Preheat oven to 165 degrees C. Grease a six-cup muffin tin.
In a medium bowl, mix together the biscuit crumbs, sugar and margarine with a fork until combined. Measure a rounded tablespoon of the mixture into the bottom of each muffin cup, pressing firmly. Bake for 5 minutes, then remove to cool. Keep the oven on.
Beat together the cream cheese, sugar, lemon juice, lemon zest and vanilla until fluffy. Mix in the egg.
Pour the cream cheese mixture into the muffin cups, filling each 3/4 full. Bake for 25 minutes. Cool completely in pan before removing. Refrigerate until ready to serve.