kyuuri to tomato wo sarada ni site, hirugohan ni tabemasu.

と is the particle used to connect nouns in an exhaustive list.

So きゅうり と トマト means cucumber and tomato.

In this sentence, it sounds like these are the ingredients being used. If you just wanted to list examples more loosely, Japanese often uses や instead, but と is the normal choice for a straightforward A and B list.

Because きゅうり と トマト works together as one noun phrase.

So:

• きゅうり と トマト = cucumber and tomato
• きゅうり と トマト を = cucumber and tomato as the object

Japanese does not need を after each noun here. The whole combined phrase is treated as the thing being acted on.

This comes from 〜にする, which often means to make something into... or to turn something into...

So:

• きゅうり と トマト を サラダ にする = make the cucumber and tomato into a salad

In this sentence, して is the て-form of する, so it connects to the next action:

• サラダ に して、昼ご飯 に 食べます
• make them into a salad, and eat it for lunch

This pattern is very common:

• 水をお湯にする = turn water into hot water
• 部屋をきれいにする = make the room clean

Here, に marks the resulting state or end form.

The idea is:

• the cucumber and tomato start as ingredients
• they end up as a salad

So サラダ にする means make into a salad.

This is different from で, which often marks a tool, method, or place. Here the sentence is not saying with salad or at salad; it is saying the ingredients are being changed into that form.

して is the て-form of します. The て-form is often used to connect actions in sequence.

So the sentence structure is:

1. サラダ に して = make it into a salad
2. 昼ご飯 に 食べます = eat it for lunch

This gives a natural do A, then do B flow.

If both parts were separate full sentences, it would sound less connected:

• きゅうりとトマトをサラダにします。昼ご飯に食べます。

That is possible, but して makes it smoother.

Here, 昼ご飯 に means for lunch or at lunchtime, depending on how you interpret it in context.

Japanese often uses meal word + に + verb to show the occasion on which something is eaten:

• 朝ご飯にパンを食べます = I eat bread for breakfast
• 昼ご飯にサンドイッチを食べます = I eat a sandwich for lunch

So 昼ご飯 に 食べます means the salad is what the speaker eats for lunch.

Because Japanese very often leaves out the subject when it is obvious from context.

So even though English would usually say I eat it for lunch, Japanese can simply say:

• 昼ご飯に食べます

The listener will usually understand the subject from the situation. In everyday Japanese, omitted subjects are extremely common.

The object is understood from the previous part of the sentence.

First, the sentence says:

• きゅうり と トマト を サラダ に して
• make cucumber and tomato into a salad

Then:

• 昼ご飯 に 食べます
• eat it for lunch

Japanese often omits words that are already clear. So the object of 食べます is basically that salad, even though it is not repeated.

Yes, きゅうりとトマトでサラダを作って、昼ご飯に食べます would also be natural.

The nuance is slightly different:

• サラダ に して focuses on turning the ingredients into a salad
• サラダ を 作って focuses more directly on making a salad

Both are understandable. The original sentence is using the grammar pattern AをBにする, which is a useful structure for learners to recognize.

Because they belong to different spelling traditions.

• きゅうり is a native Japanese word, and it is often written in hiragana in everyday contexts
• トマト is a loanword, so it is normally written in katakana

Technically, きゅうり can also be written with kanji as 胡瓜, but that is much less common in ordinary writing.

So this mix of scripts is completely normal in Japanese.

No, not in standard Japanese writing.

Normally this would be written without spaces, like this:

きゅうりとトマトをサラダにして、昼ご飯に食べます。

Spaces are often added in beginner materials to make it easier to see words and particles. They are a learning aid, not standard punctuation.

Japanese nouns usually do not show singular vs. plural the way English nouns do.

So:

• きゅうり can mean a cucumber or cucumbers
• トマト can mean a tomato or tomatoes

The exact number depends on context. In this sentence, the speaker is just talking about cucumber and tomato as ingredients, without specifying quantity.

Yes. The verb 食べます is in the polite ます-form.

Also, して is just the connective て-form, and the final verb determines the overall politeness of the sentence. Since it ends with 食べます, the whole sentence sounds polite.

A plain version would be:

きゅうりとトマトをサラダにして、昼ご飯に食べる。

That would sound more casual.