Combine the ingredients for the vinaigrette and whisk well. Season to taste with salt and freshly ground pepper.
Cook the tortellini according to the packet instructions, then rinse under cold water.Leave to drain in a sieve.
Meanwhile, prepare the vegetables. Halve the cucumber lengthways and cut it into slices, halve the tomatoes, cut the red onion into thin strips, chop the parsley and shred the lettuce.
Put the tortellini, the prepared vegetables, olives and parsley in a bowl, pour over the vinaigrette and toss well.
Crumble the feta coarsely over the salad, toss gently and finish with freshly ground pepper before serving.