Slice cucumbers half lengthwise on a cutting board. With the flesh facing up, use the flat side of a chef's knife to smash the cucumber, breaking the flesh. Chop into 1-inch pieces.
In a salad bowl, combine the cubed watermelon, smashed cucumber, berries, crumbled feta, dill, and mint.
Drizzle the dressing over the top, toss together, and serve!