Warming food in the microwave with レンチンする

レンチンする is the action of heating food in a microwave.

I figure it’s probably short for レンジでチンする. In this expression, レンジ refers to an microwave oven (electric oven), and チン refers to the sound older microwaves made to signal they finished.

Examples

Heating leftover pancakes with チンする

During Jumbo’s visit, Yotsuba tells him she make pancakes earlier.

よつば:

「まだちょっとのこってる！チンしてたべるか！？」

“There's some left over! Shall I heat it up to up to eat?”

ジャンボ:

「おう。よつばが作(つく)ったんなら食(た)べなきゃな」

“Sure. If you made them, I have to eat some.”

Lunch is heating 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!”