Use your microwave.
“Microwaves are designed specifically for heating liquid (or the liquid contained within food). Its heat waves are not wasted on heating the air or container around your food. Microwaves use 1/3 less energy than the stove. Better yet, save even more on your electricity bill by using your gas BBQ to grill more meals!”
https://www.petro.com/resource-center/spring-summer-energy-saving-tips