Naan & Namak offers a €5 lunch buffet, wow. I have paid more at the Uni mensa than at this classy Afghan restaurant! The food is excellent and the restaurant is beautiful! There is no competition in walkable distance to the university, so if you don't try it, you are certainly missing out. 25 minute walk from the Uni mensa.
I haven't been there for a proper dinner yet but based on outstanding lunch buffet, I don't doubt it is excellent.
Naan & Namak
Kopernikusstr. 82
40225 Düsseldorf
Tel.: 0211 93379980
Website: Naan & Namak