I'm listing both grass and electric types in this answer, since both are good against Lana's trial.
Rowlet/Dartrix (if that's the starter you chose)
Pichu/Pikachu (Route 1)
Magnemite (Hau'oli Outskirts)
Fomantis (Route 5)
Grubbin/Charjabug (Route 4)
Oricorio Pom-Pom form (Melemele Meadow)
Bounsweet (NPC trade- Brooklet Hill Pokemon Center [correct if wrong Location])
Morelull (Brooklet Hill)
Paras (Brooklet Hill)