Peel and finely chop the onion. Put a medium pan over a medium-low heat and let it warm for 2 mins. Add 1 tbsp oil, the chopped onion and a pinch of salt and pepper. Gently fry for 8 mins, stirring occasionally, till starting to soften.
While the onion sweats, finely chop the tomatoes into dice to match the onion. Add to the onion and fry for 8-10 mins, stirring now and then, till the tomatoes have softened and collapsed.
While the tomatoes and onion fry, peel and finely chop the garlic. Finely chop the parsley, leaves and stalks, and the mint leaves. Finely grate the zest from the lemon.
Stir the bulgar wheat into the pan with 2 tbsp water. Add the garlic, chopped herbs, lemon zest, 1 tsp tamarind paste and 1 tsp ground cumin. Squeeze in the juice from half the lemon. Give everything a good stir to mix well, then pop a lid on the pan (or use a baking tray or large plate to cover it) and set aside for 15 mins to soak. The bulgar wheat will absorb the water and the juices from the tomatoes, which will make it tender. This is your kisir.
While the bulgar soaks, put a dry frying pan over a medium heat and add the walnut halves. Toast for 3-4 mins, shaking the pan every so often, till they've started to darken and smell nutty. Tip onto a board and let the walnuts cool for a few mins, then roughly chop them.
Separate the lettuce leaves and arrange them on 2 plates. Finely chop the smallest leaves from the heart of the lettuce and stir into the bulgar wheat.
Spoon the zingy bulgar kisir over the lettuce scoops and scatter over the toasted walnuts to serve. Eat with your hands.