As it has been posted Sunday is no feijoada day. Those are Wednesday and Saturday but there are places that serve it everyday like Bolinha. Another place is Feijoada da Lana in Vila Madalena. Keep in mind that feijoada is a heavy dish, I wouldn't eat it before a long flight.
Sunday is the best day for arriving/departing GRU given lighter traffic so that will not be a problem.