The Beach course hides a secret Porygon that can only be revealed after you've unlocked the Pester Ball. As you approach the area with the three Meowth, look to your right. There's a small, rocky outcrop with a suspicious-looking bush.
Throw a Pester Ball directly at this bush. If aimed correctly, the bush will disappear, revealing a Porygon. Take several photos of it quickly before it vanishes again. This is a crucial step for completing your Pokémon Report.