Make a balsamic sysrup by pouring the vinegar and honey into a small saucepan and simmering over medium heat just long enough for it to reduce and have a thick, running consistency - about 5 minutes. Set aside, as it will thicken further as it cools.
Assemble each salad on its plate. First 1/2 cup arugula. Drizzle 1 T. olive oil on arugula. Then place watermelon plank on its side on top of arugula, put a slice of goat cheese on its side, then watermelon slice again, then another goat cheese slice, ending with another slice of watermelon. You will end up with a layered salad on its side.
Season with cracked pepper.
Drizzle balsamic reduction over watermelon, goat cheese slices.