The staple diet in Malawi is nsima, is a stiff porridge made from pounded maize meal boiled in water. Few travellers eat nsima, so it is fortunate that most local restaurants also serve rice and potato chips (or occasionally cassava or sweet potato chips).
At tourist-class hotels and restaurants in the major towns of Malawi, you can eat food to international standards at a very reasonable price.
The most widely available fish in Malawi is usipa, it is a tiny fish that is generally sun-dried after it is caught.