Good eats are cheap and you can find very good restaurants in Abidjan. You should get a vaccine for Hepatitis A before coming but even street foods are fairly clean.
maquis
Grilled "braisé" pronounced "BRA-zay" fish and chicken are very good and can be found on at outdoor restaurants called maquis pronounced "MAH-key". Try the national dishes like "alloco" and "attiéké". Alloco pronounced "AH-low-coh" is simply fried plantains, mostly accompanied by a spicy sauce called piment pronounced "PEE-monh". Attiéké pronounced "AH-check-ay" is fermented cassava yams that looks like couscous but taste slightly sour--is often served with grilled chicken or fish and vegetables tomatoes, onions, cucumber and a must-try. Usually white rice or french fries are starchy alternatives to alloco and attiéké as side dishes. Another specialty is the excellent "shougouilla" a blend of charbroiled meat! You can always ask for extra vegetables, especially avocados, which are amazing during the season.
Service can take a while at a maquis -- typically women cook and sell the food and men sell the drinks, so don't be surprised if you're billed separately for food and drinks. Since one typically eats with one's hands at a maquis, usually they will have a sink or offer a bucket and soap for hand washing before and after you eat. Note that locally people eat only with their right hands and kleenex are used for napkins.
la nourriture "végétarienne"
Be aware that it's common for locals to say that dishes containing chicken or fish are vegetarian since they don't have "meat" in them, so it's helpful to clarify if you're looking to avoid it.
other kinds of restaurants
You can find most typical maquis food at more mainstream restaurants too, usually mixed with standard French and international dining options. In Abidjan, Lebanese food is another good offering, and there are several fancy and expensive French restaurants that are very good. Vietnames nems fried spring rolls are very popular and cheap.
When in doubt, skip getting a burger, local beef is very dry. Fish and lobster are usually freshly caught if you're near the coast. Fresh fruits, like mangoes, pineapple and papaya are everywhere, and are the best in the world when in season.
tipping
A service charge is not included in the bill, and usually it's seen as acceptable to tip at a flat rate of 500-2000 CFA, depending on the size of the group and effort of the waiter.