For the dressing
Cut the tomatoes into bite-size chunks, discarding the cores. Cut the cucumber in half crossways, then cut a cross in the end of each piece and cut into quarters. Cut the quarters crossways into bite-size pieces. Peel the onions and cut into thin wedges. Shred the lettuce.
Whisk the dressing ingredients together in a jug. Put all the salad vegetables in a large bowl, add the olives and toss the ingredients together using your hands.
Pour the dressing over, and toss gently to mix, then crumble over the feta cheese. Serve immediately