Hands down the most commonly devoured dish during this season is none other than Hiyashi Chuuka. Once summer comes around, these dishes hit all restaurants and conbinis.
Although, if you can find a do-it-yourself pack at the market, that would probably be the best (and cheap). It's a simple dish to prepare: cut up cucumbers (or other desired veggies), scrambled eggs and meat (I like to use ham), then boil the noodles for a couple minutes and rinse out with cold water. Then all you have to do is transfer everything into a boil and pour the sauce contents over and BAM, a savior for summer hunger pangs. I chose to fry some additional gyoza to compliment.