Here are a few restaurant suggestions for Penzance, Newlyn and Mousehole, perhaps also look at Trip Adviser which has up to date reviews and descriptions of many more restaurants, my selection is based on personal experience and also suggestions from guests:
Chapel Street is the oldest street in Penzance and is arguably the best place to look for restaurants in town. Two Pubs serving food are The Turks Head and The Admiral Benbow, Restaurants: Blacks, The Bake House, Artist’s Residence
elsewhere in Penzance:
Alverne, Camelot Court, 30 Alverton St
Mermaid Alley, 45 New St.
Thai: Thai Moon (2 Alexandra Road, two minutes’ walk from Treventon)
Mackerel Sky, Tapas sized fish dishes. Very popular and does not take bookings.
The Bridge, Pasta & Pizza, opposite Mackerel Sky.
The Tolcarne Inn (Pub Restaurant)
Jelberts, just their own vanilla ice cream optionally with clotted cream and flake. Eat it Ocean side by the fisherman statue.
The Old Coastguard. By the carpark at the top of the village.
2 Fore Street. On Fore Street by the harbour. On a warm day a takeaway eaten on the harbour wall or suitable rock is bliss, of course accompanied with a takeaway drink from the pub.
The Ship Inn. Harbour side pub & restaurant.