Combine all the ingredients except for the chopped spinach in a large mixing bowl. Mash with an egg or potato masher (a fork would also do the trick) until well combined.
Using a spoon this time, delicately stir in the chopped spinach.
You can serve this salad immediately but it greatly benefits from a short stay in the refrigerator. It can also be made up to a day in advance and will keep for up to 2 days in an airtight container.