Alappuzha has good Kerala food and some excellent fish. The local speciality is karimeen — pearl spot fish — caught in the backwaters and typically cooked in a banana leaf with a spiced masala. Most guesthouses and mid-range hotels serve a thali at lunch that is a reliable and cheap way to eat well.
Thaff Restaurant on Mullakkal Road is one of the best places for non-vegetarian Kerala food — try the karimeen pollichathu and the prawn curry. Harbour Restaurant, near the beach, does good seafood at reasonable prices. For a more local experience, the small meals stalls around the boat jetty serve rice and fish curry for next to nothing.