This achievement can be unlocked in "Angel Oracle" in the 2nd half of the game.
I recommend creating a separate save file when you first enter "Angel Oracle" since there a 3 story-related achievements in total. Depending on your choices all of them can be missable.
Here are the things I did, to unlock this achievements. There may be other ways too, but if you follow these steps you will definitely get this achievement. Keep in mind that you need certain skills at 7+, like mechanic, lockpicking, demolition or some of the talking skills to get to this achievement. Things I did, prior to unlocking this achievement:
1. When you enter the area, walk right and talk to the hobo, who tells you about the meat in angel oracle.
2. Before you enter the premises talk to the guards and tell them about the hobo.
3. When you are inside, go to the kitchen and talk to the chef. Use your talking skills to unravel the truth behind the meat they are eating.
4. Go to the left of the kitchen, pick the lock and sabotage the fridge. Open it and examine the things in the fridge.
5. Go down the stairs and to the cage. Talk to the prisoner. Go back up the stairs. Someone will tell you, that the prisoner has escaped and you have to hand over one of your teammates to compansate for the lost prisoner
6. In front of the cage you will find some footprints follow them and talk to Roger Yee, who will send you to Gen Cronk. Cronk will reveal the hideout of the prisoner. Go there and get to him before the robots have a chance to kill him.
7. Talk to him and tell him that one of your camarades has been captured in his stead and he will agree to go back.
8. Back in Angel Oracle go down the stairs again and witness the whole shabang thats going on around the execution. (THIS IS THE POINT OF NO RETURN)
9. Speak to Mr. Manners and tell him that Tori is plotting against him. (This will unlock "How Rude").
10. Go and see Mr. Manners again in his "appartement" and tell him about the cannibalism. It is hard to convince him, but he will eventually give a trade contract for beef (alternative meat) to you.
11. Go and see the dentist at his place (which is located north-east of Angel Oracle), don't kill or attack anyone or anything there. Talk to him and tell him about the trade contract. He will shoot one of his cows and give you a sample of the beef.
12. With that beef, go back to Mr. Manners, hand him the sample and he should agree to chnage the source of meat.
Hope this helps guys!
Any improvements? Please let me know in the comments below!