Stir in the lemon juice and the wine and as soon as it has boiled for a couple of minutes add a tbsp of mustard, the zest, plenty of oregano, salt and freshly ground pepper. If you see that the liquids don't cover the meat add a little water (careful, not too much because it doesn't evaporate easily from the pressure cooker and you will end up with a soup!). Lock the lid of the pressure cooker and when it starts to boil turn the heat down.