Food is the most important thing for the people, and the chef's following techniques have undergone chemical changes: (a) Lamian Noodles B. Cut pumpkin C. Cook a carp into Wanzhou grilled fish D.

A, noodles just changed in shape, which belongs to physical changes, so A is wrong;

B, cutting the pumpkin just breaks it, and no new substance is produced, which is a physical change, so B is wrong;

C. Cooking a carp into Wanzhou grilled fish produces new substances, which belongs to chemical changes, so C is correct;

D, washing vegetables only removes impurities, and no new substances are generated, which belongs to physical changes, so D is wrong.

So choose C.