This is the 3590th most frequent German word.
mittagessen
Lunch.
In this sentence, 'Mittagessen' is used as a noun referring specifically to the midday meal, which is its primary usage in German.
Wir essen heute Mittagessen um 12 Uhr.
We are eating lunch at 12 o'clock today.
Here, 'Mittagessen' is in the accusative case, being the direct object of the verb 'vorbereiten'. It signifies the meal to be prepared for consumption at midday.
Könntest du das Mittagessen für morgen vorbereiten?
Could you prepare the lunch for tomorrow?
In this instance, 'Mittagessen' is used as a subject, described and referred to with the relative clause 'das ich gestern gegessen habe.' It acts as a general identifier for the meal.