this invention wasn't made because someone was trying to find a better and faster way to cook, it was kind of an accidental invention made during the world war 2.
during the war two scientist invented a magnetron, which is a tube that produces microwaves, but not the one that is able to cook food, the microwave they invented was able to spot the Nazis war planes that was coming their way.
many years later Percy LeBron spencer discovered that the microwave was able to cook food as well as help out in the war, this was found out when the radar waves coming from the microwave, melted some candy bars that was in his pocket
when the first microwave oven was in the market it was as big as an average refrigerator now. and it had become very popular over the years and had improved many by today.