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!"