issyo ni okonomiyaki wo tukurou.

It is read:

いっしょに おこのみやきを つくろう。

Word by word:

• 一緒に = いっしょに
• お好み焼きを = おこのみやきを
• 作ろう = つくろう

A natural full reading is:

いっしょに おこのみやきを つくろう。

一緒 means together.

The に turns it into something like an adverbial expression, so 一緒に means together, with each other, or together with someone in the sentence.

So:

• 一緒 = together / same
• 一緒に = together, jointly

In this sentence, 一緒に tells you how the action is done: making it together.

を marks the direct object of the verb, meaning the thing that is being made.

So in:

• お好み焼きを作ろう

the お好み焼き is the thing being made, and を marks it as the object.

You can think of it roughly as:

• お好み焼き = okonomiyaki
• を = marks okonomiyaki as the thing acted on
• 作ろう = let’s make

作ろう is the volitional form of 作る.

• Dictionary form: 作る = to make
• Volitional form: 作ろう

The volitional form often means:

• let’s make
• shall we make
• sometimes I’ll make depending on context

In this sentence, the natural meaning is Let’s make okonomiyaki together.

For a る-verb, the volitional usually ends in -よう, but 作る is actually a godan verb, so its volitional becomes 作ろう, not 作よう.

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

So even though English usually says We should make okonomiyaki together or Let’s make okonomiyaki together, Japanese often just says:

一緒にお好み焼きを作ろう。

The listener understands that the speaker means something like:

• Let’s make it together
• You and I should make it together

This omission is very normal in Japanese.

Yes, 作ろう is a casual way to say it.

A more polite version is:

一緒にお好み焼きを作りましょう。

Comparison:

• 作ろう = casual, friendly
• 作りましょう = polite, more formal

Both can mean Let’s make okonomiyaki together, but the tone is different.

Japanese sentences usually place the main verb at the end.

So this pattern is very common:

[time/place/manner] + [object] + [verb]

In this sentence:

• 一緒に = together
• お好み焼きを = okonomiyaki + object marker
• 作ろう = let’s make

This verb-final structure is one of the biggest differences from English.

お好み焼き is the name of the dish itself: okonomiyaki.

In this word, お is part of the standard word, not something you should remove in normal usage. So you normally say:

お好み焼き

not just 好み焼き.

The word is built from:

• 好み = preference / liking
• 焼き = grilled / cooked

So the dish name has the idea of grilled as you like it or cooked to your taste.

Yes. 一緒に can mean:

• together
• with
• along with

The exact English translation depends on context.

For example:

• 友だちと一緒に行く = go together with a friend

In your sentence, 一緒に naturally means together, because the sentence is inviting someone to do the action jointly.

Grammatically, the volitional form can sometimes express the speaker’s own intention, like I’ll make. However, in a sentence like this, especially when spoken to someone, the most natural interpretation is:

Let’s make okonomiyaki together.

Because of 一緒に and the conversational context, it sounds like an invitation or suggestion more than a statement of personal intention.

No. Normal Japanese is usually written without spaces:

一緒にお好み焼きを作ろう。

The spaced version is often used only for learners to make the parts easier to see:

• 一緒 に お好み焼き を 作ろう

In real Japanese writing, you would normally write it as one continuous sentence.