1. Combine cooked pasta, chicken, tomatoes, cucumber and onion in a large bowl.
2. In a seperate bowl, stir together lemon juice and salt until the salt dissolves.
3. Add olive oil and oregano, mixing well.
4. Pour over pasta mixture.
5. Stir to blend.
6. Add feta cheese and olives.
7. Toss to mix.
8. Cover and chill for 2 hours before serving.