There are many theories, but other than avoiding being overweight, there's a lack of good scientific evidence for any specific diet.
The important things are a normal healthy diet, with plenty of fruit, veg, and fibre. You might have to drop fruit, veg, and fibre during radiotherapy, so making sure you weren't deficient beforehand is probably a really good thing.
That's not to say ignore the theories - mostly they're harmless at worse, and there's a chance some might be better than harmless. On this basis there's some suggestions consuming tomatoes, broccoli, turmeric, and pomegranate may be beneficial. There's also a suggestion dairy might be bad, but being on hormone therapy, it's really important you aren't deficient in calcium for which dairy can be a significant source.
I'm not avoiding dairy.
I have also bought a supplement a retired urology consultant suggested called Pomi-T, which is Broccoli, Turmeric, Pomegranate, and green tea extract. I wish it didn't have the green tea extract which is known to cause liver failure in large doses and also brings in caffeine which I didn't consume even before PCa, but the dose of both of these is very small. I probably won't buy anymore.
There is evidence for plenty exercise being beneficial in slowing many cancers including prostate. It also leaves you in a better health to handle many of the treatments, and can play a part in avoiding being overweight. It's also important to be stressing bones when you are on hormone therapy, with jogging and weights being the most beneficial. I do it via cycling. Exercise is probably much more important than a specific diet.