I got curious about this and did a google map search of Magens Bay. Apparently there is a place there called the Tropic Leisure Club at Magens Point Resort, but I can't tell how close it is to the beach. I was not previously aware of this but then I've not been to Magens Bay in quite a while. It says the restaurant is the Rumbuzz but the restaurant link is no longer live. Magens Point Resort | Resort Overview
There is a snack bar on the beach that serves burgers and pizza. I do not know if it is affiliated with the resort.