First, start by dicing your watermelon into bite-sized cubes, thinly slice your red onion, chop or slice your Kalamata olives, and roughly chop the fresh mint. Set them all inside a large mixing along with the feta cheese crumbles. 

Next, in medium mixing bowl with a whisk, combine the lemon juice, olive oil, and lemon zest. Whisk everything together vigorously to create a simple vinaigrette. 

Last, pour the dressing over the watermelon in the large mixing and give the salad a quick toss to coat all the ingredients before serving. Sprinkle with salt and pepper to taste.