passive in noun modifier

Question

I understand the use and structure of a noun modifier using standard masu plain past form, eg たなかさんが　かったすしは、... etc. etc. The sushi that Tanaka bought... etc. Now it's noun modifier with subject ga, masu verb in plain past, modifying the noun, sushi.

I get that in passive it's the object that's being highlighted, that now forms the subject. And I get direct and indirect passive sentences. No worries.

But what are the rules for using passive to modify a noun and why and when is it preferred over plain masu form?

1. わたしが　たべた Pizzaは きのうのばん　ともだちに　つかいました。 ok all good.

2. たべられた　Pizza は　おいしかったです。/ or should I use a noun to finish sentence, よくham and pineapple です、

I am not really understanding why No2 in passive, is wrong.

Answer 1

It's not about logic, but is more to do with the availability of other expressions.

1　わたしが　たべた　ピザは 　おいしかったです。
2　たべられた　ピザは　おいしかったです。

The #1 straightforwardly makes sense.
The #2 is hard to process what it's saying. :) When you want to say an unusual thing and express the pizza as something being eaten, we would try to make it clearer and say something like

3 わたしに　たべられてしまった　ピザは　おいしかったです。

But again, this is an unusual thing to say.

When you want to say 'a pizza that you were able to eat,' this could be:

4 （やっと）わたしが　ありつけた　ピザは　（それでも）おいしかったです,

In other words, we usually want more expressions, modifiers, adverbs in the sentence. However, if you say わたしに instead of わたしが, it becomes more natural even without additional modifiers:

5 わたしに　たべられた　ピザは　おいしかったです。

In this way, it can naturally sound like talking about what you've been able to eat than what has been eaten by you. The reason could be your health condition.

Answer 2

(1) There are no explicit 'rules' in any language for when to use active and passive. You can express a range of concepts using either, or both. Consider the sentences:

"Stephen King wrote that book".
"That book was written by Stephen King".

There is no semantic difference there, only a stylistic one (if any). Both sentences are grammatically correct and neither one is better than the other. There are no specific rules which dictate whether you should use one or the other. The same is true for Japanese.

(2) Modifying a noun with the passive form depends on what the speaker is trying to express. When the need to use it arises, then it should be used. One obvious example would be when the 'doer' of the verb is not known. In that case it might be more difficult to construct an active sentence as it might sound somewhat artificial. So a passive construction might sound more natural. Maybe something like 昨日発表されたキャンペーン ("the marketing campaign which was announced yesterday") if you don't know who actually made the announcement but still want to talk about it.

(3) Care is needed with passive constructions, because as pointed out in other comments, it can be confused with the potential forms - 食べられる could be passive or potential, depending on the context and grammar.