Chop the watermelon, cucumber, and feta into bite-sized pieces of roughly the same size - 1/2 inch cubes.
Slice the red onion into thin strips. Add the cucumber, feta, watermelon, and red onion to a large mixing bowl.
In a separate bowl, combine the honey, red wine vinegar, salt, pepper, and olive oil. Mix well. Pour the dressing over the watermelon and cucumber mixture. Toss so that the dressing covers the entire salad. Top with fresh mint.