"The lunch is tasty."
Translation:Obiad jest smaczny.
Each noun in Polish has its grammatical gender: male, neutral or female. Adjective has to fit its form to the gender and the case of the noun it describes.
- "Obiad" (lunch/dinner) is male, so the adjective has to be in male form "smaczny obiad".
- "Zupa" (soup) is female, so it would be "smaczna zupa".
- "Mięso" (meat) is neutral, so it would be "smaczne mięso".
Because the trick with using "to + noun in nominative" instead of "jest + noun in instrumental" can be done only in structures "noun is noun" 
See my comment to 94BlueLane's question.
 To be more precise, it can be also done with other words or groups of words, as long as in a sentence they perform the function of subject as a noun or a noun phrase. Perhaps also the function of object, but I can't think of any case where no "real" noun would be used as a part of object.
This is true for phrases type Subject-Verb-Object, where object can be either a noun, or a noun described by some adjectives (noun phrase). In that case, the verb "jest" governs the object and requires instrumental case:
- Pies jest zwierzęciem. - The dog is an animal.
- On jest dobrym człowiekiem. - He is a good man.
The above is a different case: Subject-Verb-Adjective. We do not have an object (or another noun besides the Subject), we only use the adjective to describe the Subject. In this structure there is no instrumantal case, only the adjective in nominative:
- Pies jest miły - The dog is nice.
- On jest dobry - He is good.
100% true!! Obviously they're not real Polish words, but they liked them anyway :) Maybe it's a Łodz thing? Reply: i would assume Antonina was referring to the noonish/lunch meal. I miss her schnitzels and kotlety :( also weird was how 'makaron' was used for all pasta including noodles :/