If it really was "my wife's lunch", that's "obiad mojej żony". My wife goes into Genitive for possession.
Sort of an inbetween one (regular in the endings at least, like everything), declines like its root: "nieść"
"With nieść and móc, the o of the stem becomes ó in the third-person singular masculine. With nieść, the o of the stem becomes e in the masculine personal plural."
Swan, Oscar (2008-10-12). Polish Verbs & Essentials of Grammar, Second Edition (Verbs and Essentials of Grammar Series) (Kindle Locations 1354-1357). McGraw-Hill Education. Kindle Edition.