FatBoys has gone halal under the name FatPapas! They operate out of a two-story shophouse along Bali Lane. It is opened till 11pm every day, so if you don't feel like eating murtabak, this is a good alternative nearby.
I ordered what I'd usually order at FatBoys, the Wimpy, and it tasted as good as the non-halal version. The thick and juicy patty, turkey bacon, and sesame bun complimented each other very well.
A good portion of the menu items are the same as FatBoys though there are some differences. The biggest one is that they don't have the Fat Basterd, which is basically a double patty Wimpy. You can still add a patty if you wanted to but at a slightly more expensive price. (Rating:😬)