In this sentence, it is used the Subject+是⋯的 structure. Between 是 and 的 you can use nouns, verbs, adjectives, or little phrases, with different meanings.
In the sentence given, between 是 and 的 we have the verbal phrase 用爷爷的番茄、生菜和黄瓜做 (as imkzh and Jason Swift correctly said, grammar rules would have "、" instead of "，") made of the prepositional phrase 用爷爷的番茄、生菜和黄瓜 and the verb 做 (thank you @dan for pointing this out).
The verb (verbal phrase in our case) in the structure 主+是+动+的 describes or classifies the subject (主).
Edit about the 主+是⋯的 structure
(From the book《现代汉语八百词》. The following list is not complete. It does not include other uses of the structure, including the one for emphasis, each with its own peculiar features.)
Can it be a 主(S) + 谓(V) + 宾(O) structure?
It is not correct to consider 是 as the predicate and 用爷爷的番茄，生菜和黄瓜做的 as the object. That way, we would ignore the very existence of the 是⋯的 structure. As explained in the same book cited above, a 的 phrase ('的'字短语) preceded by 是 forms the 是⋯的 structure functioning as predicate.