Learn Turkish: Sağlık için bol sebze yemek lazım. - It is necessary to eat plenty of vegetables for health.

This is the structure for general necessity! To say 'It is necessary to [do something]' in general, you just use the infinitive (the dictionary form ending in -mak or -mek) followed by lazım. Here, yemek lazım means 'it is necessary to eat' without pointing to a specific person.

The English translation says 'vegetables'. Why isn't it plural (sebzeler) in Turkish?

In Turkish, when a noun is preceded by a word that already indicates quantity or amount—like bol (plenty/a lot)—the noun itself stays singular. Therefore, it is bol sebze, not bol sebzeler.

Is için working like the English word 'for'? Why is it placed after sağlık?

Yes, için means 'for'. But unlike English prepositions that come before a noun, Turkish uses 'postpositions' that come after the noun. So 'for health' is built as sağlık için (literally: 'health for').

I have learned that yemek means 'food'. Is it a noun or a verb in this sentence?

In this sentence, it is the verb 'to eat' in its infinitive form. The word yemek is special in Turkish because it functions as both the verb 'to eat' and the noun 'food' or 'meal'. You can tell it is the verb here because it is part of the -mak lazım grammar structure.