Heat oil in a saucepan then saute onion until translucent. Stir in tomato, cook for 1 minute. Stir in rice, pine nuts and herbs, lemon juice and vegetable stock. Bring to a boil, stirring. Cover then simmer until stock is absorbed by the rice.
In a saucepan of boiling water, drop in the vine leaves, two at a time. Remove after 5 seconds then rinse in a colander. Lay out flat then spoon in about a teaspoon of the rice into each. Roll up tight.
In a bowl, mix yoghurt, lemon juice and cucumber. Cover and set in the fridge.
Line a saucepan with some extra vine leaves. Place the dolmades into the saucepan, cover with 1 cup water then bring to a boil. Reduce heat to very low, cover then simmer fro 1 1/2 hours. Remove from heat then allow to sit, covered for 2 hours, until all water has been absorbed. Serve with yoghurt sauce.
For a vegan substitute, use soy yoghurt instead of a dairy based yoghurt.