From Halopedia, the Halo wiki
A moa nugget is a type of food made from the meat of a moa, an avian species native to Reach. Moa nuggets were once a simple staple in the KolonyKids Meals of Have S'Moa, a restaurant and petting zoo owned by Wiljax Brantley on Gannick 22. Following the glassing of Reach in 2552, Brantley had ownership of the largest population of remaining moa in the galaxy. Thus, the moa nuggets became an incredibly expensive delicacy among wealthy Unified Earth Government dignitaries.
Moa nuggets are a reference to chicken nuggets, a modern-day food product commonly associated with McDonald's.