Mix the flour, oil and salt with enough cold water to bring the mix together into a wet dough which comes away cleanly from the sides of your mixing bowl. The dough should be easily manipulated and stretchy, but not stick to your fingers.
Simmer the lentils together with the olives, oregano, chopped tomatoes and all the juices from the tomato can, once you've chopped the tomatoes. Do this for 5-10 minutes over a medium heat.
Line your pudding basin with approx half to 1 cm thick layer of pastry (keeping ⅓ for a lid, then fill with the tomato and onion and olive mix, and then use the remaining ⅓ as a lid.)
This will only fill your basin to approximately ¾ full, but don’t worry, it will grow when you steam it.
Place a pleated piece of foil over the top and tie it around the rim (illustrated, right) and steam for approx 2-3 hrs in the slow cooker, or on your hob in a bain marie until the pastry is bulging above the top of your pudding basin.
Serve with 80g carrots per person and 200g potato per person, made into wedges.