Notes for Parsley and Mint - The parsley can be chopped ahead of time just like the tomatoes. They will stay fresh in the fridge for up to a day if stored properly. Parsley should be stored in an air tight container while tomatoes can be kept in a strainer set over a bowl and covered well with plastic wrap. Mint can discolour if chopped too early, but I chopped my mint a day early and it seemed perfectly fine overnight in an airtight container.
Notes for adding Lemon Juice - The amount of lemon to be added depends on your taste. I recommend adding juice of half a lemon first and adding more if you prefer more.