Either dice the chicken breast very finely with a knife or chop it into small pieces with a cleaver, similar to coarse minced meat. Mix the meat with the lime juice and marinate for about 10-15 minutes. Sear it in a pan without adding any fat and finish cooking. The liquid in the pan should have evaporated.
In the meantime, cut the soft part of the lemongrass very finely, finely dice the galangal. Finely chop the shallots, celery, spring onions, coriander, mint and chili peppers and set aside.
Season the chicken with fish sauce, sugar and chilli flakes. If necessary, re-acidify with lime juice and let cool down lukewarm. Now mix the meat with the shallots, herbs, etc. and arrange on the lettuce leaves. Cut the cucumber into slices or lengthways strips and serve with the laab and jasmine rice.
Sprinkle 1 - 2 tablespoons of rice semolina over the finished Laab as desired. You can easily make your own rice semolina by carefully roasting raw rice grains until golden yellow in a pan without fat. Stir constantly, then allow to cool and pound in a mortar (grain size like coarse semolina). The rice semolina can be kept for several months in a closed glass.
Laab tastes best when the meat is generously mixed with the herbs mentioned and served lukewarm.
The quantities of fish sauce, chilli flakes and chillies are only indicative, the same applies to the quantity: if only laab is served, the quantity is sufficient for approx. 2 people, if additional dishes such as soups and curries are on the table, the quantity is sufficient for 4 - 6 people.