First, make your crumble topping - in a food processor mix together the oats, flour, butter and sugar. Set this mix aside in a bowl and clean the food processor so you can make up the buttery biscuit base.
Do this by blitzing the biscuits first then pouring in the butter until the mixture looks damp but not wet. Set aside.
Whisk together the sugar with cream cheese until the mixture is smooth, then add eggs and briefly keep whisking. Finally, whisk in the vanilla and lemon zest.
In a lined cake tin press down the buttery base - make sure its solidly pressed into all the corners. Pour over the raspberry/cheesecake mixture and smooth down. Sprinkle over the crumble mixture and bake for 45 mins to an hour at 160°C/340°F.