I know we are in Istanbul to take advantage of its restaurants and terrases by getting out of our homes after work ;) ..but again if you are tired and would just order something(from relatively diverse cuisines) that could be delivered to you anywhere in Turkey, you can use the below web site.
You can choose the turkish or english version from the upper right menu :)
Once your account and adress is set , you choose the region of Turke you are in then you have access to a variety of restaurants in that region/district.
You can also verify if the restaurant is closed or open then check the minimal order for delivery (that if you "mouse over" the different restaurants )
PS: hope this is not the 37 th time this site is being posted ;)