Place the butter in a pan along with all the other ingredients up to and including the lemon juice, bring to the boil while stirring occasionally. Remove the pan from the heat. Add the oats, mix well, transfer to the prepared tin.
Approx. 40 mins. in the centre of an oven preheated to 160°C. Remove from the oven, allow to cool slightly, remove from the tin and leave to cool on a rack. Cut into approx. 16 equal bars using a bread knife.