Cut the watermelon and feta into cubes, roughly ½ inch each – you want them close to the same size so the checkerboard pattern lines up nicely. For the feta, use a sharp knife and cut slowly – real Greek feta is firm but it can crumble if you rush it. Make sure the cubes fit your olives size.
Start arranging on a flat board or a wide shallow plate. Place a watermelon cube, then a feta cube, then an olive, and keep alternating to build your checkerboard pattern. Take your time with the first row and the rest falls into place easily.
Once the board is arranged, drizzle a few drops of olive oil over the top if you’re using it, then finish with a generous sprinkle of dried oregano. That’s really it.
Stick a few toothpicks into some of the cubes so guests can easily pick them up without touching the whole board. That’s really it.