Peel and cut the watermelon into 1-inch cubes using a chef's knife on a cutting board. Arrange the cubes in a large mixing bowl.
Crumb the feta cheese into small pieces and sprinkle evenly over the watermelon cubes.
Roughly chop the fresh mint leaves and add them to the bowl with the watermelon and feta.
Using a citrus juicer or reamer, extract the juice from the lime. Pour the lime juice over the salad, then toss gently with a large spoon until all ingredients are evenly coated.
Inspect the salad, ensuring the feta and mint are well-distributed, and the watermelon is coated with lime juice. Serve immediately for the freshest flavor and crisp, refreshing texture.