The best way by far is to just use load of stone and try to keep it eating a all times. I tried stone structure for a level 145 and I made 36 structures and it only went up 7 percent. I used a ton of stone for the same gacha and it tamed in under 5 minutes (don't drop them one by one)
I wanted to add this because I had to look EVERYWHERE to find out why my Gachas wouldn't eat to tame up!
Gachas who are in the vacinity of other Gachas (live or dead) sometimes will not eat the things you throw on the ground for them. Go ahead and kill the other Gachas(s) than the one you want to tame harvest the corpse(s), move out of render distance, return and try again.
Gachas who have recently been in combat also will sometimes not eat things thrown on the ground. Kill any hostile creatures in the area, punch the Gachas, move out of render distance, return and try again.
This last bit is just speculation because it needs more testing. I believe metal doorframes may provide less taming effectiveness than other metal structures. I would've gotten a 135 Gacha to lvl 202 with metal walls but using doorframes it tamed at 200.