It wasn’t until I worked at a wedding reception hall that I found this cutting technique. I used to cut wedges, then cut small lines in the wedge and get the squares that way, but this is SOOO much faster. I don’t know if I could explain how to do it better than a picture, so I did a step by step photo sequence to help you out.
With your melons, make “Sprite Salad” recipe here. Hint: Contains no Sprite.