Do we talk about now or in general?
If you want to say "are you going to the restaurant to which Mehmet always go?", then this way is better: "Mehmet'in her zaman yemek yediği lokantaya mı gidiyorsun?"
If you want to talk in general, not for the moment, then your translation is correct (Except that we dont use apostrophe for lokanta. If a noun starts with a lower case, then dont use apostrophe.)