All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
A person who is religiously required to pay Zakatul-Fitr has to pay it out according to what is prescribed in religion, which is a Saa' (2,480 grams) of dates or one Saa' of barley. It is confirmed that Ibn 'Umar said: "The Prophet enjoined the payment of one Saa' (2,480 grams) of dates or one Saa' of barley as Zakatul-Fitr on every Muslim, free or slave, male or female young or old." [Al-Bukhari] So if one wants to be more generous to the needy by giving them Zakatul-Fitr cooked, then there is no harm on him, Inshaa' Allaah. However, he has to ask their permission on the matter. If they want to take Zakat [food] before it is cooked, then he has to give it to them uncooked, and if they want it cooked, he can cook it for them.
Allaah knows best.