Chullin 37b quotes Yehezkel as saying:

לא אכלתי בשר כוס כוס מעולם

I have never eaten meat [with] couscous.

Why would he not eat this dish? What’s wrong with eating meat and couscous?

This question is Purim Torah and is not intended to be taken completely seriously. See the Purim Torah policy.

Very simple - he was vegetarian!

The continuation of the Gemara there explains that he received a psak that it is forbidden to eat meat altogether:

ולא בא בפי בשר... שלא אכלתי מבהמה שהורה בה חכם

No meat ever entered my mouth... I never ate from an animal, because a wise man instructed me [not to].

Who was this wise man? It must have been Rav Kook (see Leather and vegetarianism according to Rav Kook?).

The posuk says נותן לחם לכל בשר, implying that the only grain-based product that can be eaten with meat is bread. Couscous is in a different category, מעשה קדרה, so it's excluded.

(In fact, Yechezkel may have held like one understanding of Beis Shammai's opinion (Berachos 42b) that bread and מעשה קדרה are so different that the bracha on bread doesn't exempt מעשה קדרה eaten in that meal.)