Who owns the restaurant? Do they work for free too? Seems like a scheme for the rich "haves" to employ an unlimited pool of poor "have-nots" for free, allowing them to get richer while the poor stay poor on a fixed income.
What is going to entice those restaurant workers to actually work? If they can get their UBI check only in exchange for work, then it's not UBI, it's communism: everyone works for the government and the government contracts out its workforce to capitalist owners, or assigns them as desired. But that can't be, as the whole premise of UBI is that there are not enough jobs to go around; the purpose of UBI is to provide for those that cannot work. So work becomes voluntary as people compete for the privilege of working. But who is going to volunteer to do the dirty jobs?
Seems like you want UBI + wages. You get your UBI automatically just because you're alive, but workers still get paid wages. Get fired, no wages. That incentivizes work, spreads the wealth out from the owners who don't get to just keep all the profits for free, while still supporting those who are unable to work. Only the best will be employed, and wages will mean more since they are pure profit -- UBI covers your cost of living. On the other hand wages can be very low since they are gravy, still letting the fat cats make obscene profits, and since it is an employer's market they can exploit workers with long hours and mistreatment. After all, there is a long line of others willing to endure the abuse in exchange for an extra buck or two.
This looks very dystopian no matter how I slice it.