Lunch is heating with レンチンする

Vocabulary Explanation: Warming food in the microwave with レンチンする

Satsuki is left to watch Sara for the day. As the afternoon arrives, Satsuki discovers their lunch had already been prepared and placed the refrigerator, with a note saying to heat it and eat it.

皐(さつき):: 「今(いま)　レンチンしてるから待(ま)ってね〜」; “The food's heating up right now, so wait a bit, okay?”
サラ:: 「わーい！」; “Yay!”

Key Points

1レンチンする means to microwave

レンチンする is casual slang for heating food in a microwave.
It comes from レンジ plus the “chin” sound associated with a microwave finishing.

2レンチンしてる describes an action in progress

してる is the casual contraction of している.
Satsuki is saying the food is currently being heated, so Sara should wait.

3から gives the reason for 待(ま)ってね

The first clause explains why Sara needs to wait: lunch is heating right now.
待(ま)ってね is a gentle request, softened by ね.