Previously in Sun and Moon, Hala was one of the Elite Four members, but he’s since been replaced by Molayne. That said, you can fight Hala at his full strength by heading over to Iki Town and finding him near the entrance.
Island Kahuna Hala
Hala has evolved his Makuhita into Hariyama–a brawler with high HP and Attack, but otherwise shockingly bad stats. It can use Fake Out for a first turn flinch, Close Combat for STAB, Knock Off to hurt Psychics and Ghosts, and Heavy Slam to pulverize Fairies. Flying-types are recommended.
Likewise, Hala’s Machop has evolved into its final form, Machamp, which boasts excellent Attack and reasonable bulk, but has low Speed. This one can use Cross Chop for STAB, and Fire, Thunder and Ice Punch to combat a variety of common Types. Psychic and Fairy-types are the safest choices.
Bewear is an evolved Stufful with similar stats to Hariyama. Its Fluffy Ability weakens contact moves, but makes it weak to Fire. For attacks, it has Hammer Arm for STAB, Brutal Swing and Shadow Claw to hurt Psychics and Ghosts, and Dragon Claw as a party trick, maybe? Hit it with Flying, Fighting or Fairy-types.
Poliwrath is one of Poliwag’s fully evolved forms, possessing well-balanced stats outside of its mediocre Speed. Hala’s can use Waterfall and Brick Break for STAB, Poison Jab to knockout Fairies, and Payback to beat up Psychics and Ghosts. Grass, Electric and Flying-types are all favorable picks.
Finally, Crabominable has stunning Attack, but suffers from the typical problem of low Speed. It can use Ice Hammer and Close Combat for STAB, Stone Edge to down Flying-types, and Earthquake to bash up Flying-types. It’s also equipped with Fightium Z. Psychic and Fairy-types are strongly recommended.