Rinse your pearl barley till the water runs clear. Place in a lidded pan with enough water to fully cover. Add a pinch of salt. Bring to the boil. Pop a lid on. Lower heat.
Simmer 20 mins or till the barley is fully tender. Drain. Rinse under cold water.
Strip the leaves from your thyme. Place on a cutting board with your pitted olives. Finely chop. Fold through the barley.
Halve the smaller and quarter the larger tomatoes. Mix with a pinch of salt in a bowl. Massage the salt into the tomatoes with your hands till some of the juices start to come out. Fold through the barley, along with the watercress (plucking any larger, tougher stalks out).
Season with a hit of black pepper. Add a gloss of olive oil. Taste. Tweak and serve.