Cook the couscous according to the package instructions. Usually it simmers, covered, in 1 1/4 cups boiling water for about 8 to 10 minutes until the water is absorbed. Put the hot couscous in a bowl and add the olive oil, lemon, sea salt and pepper. Give it a toss to combine and set aside. Add the vegetables, parsley and mint to the couscous and toss well. Taste for seasoning and refrigerate the salad for at least a couple of hours to chill thoroughly. Sprinkle in the feta, and the pine nuts and olives if using, when you are ready to serve.