Watermelon Salad with Feta and Mint

1/3 cup extra-virgin olive oil 3 tablespoons fresh lemon juice 2 teaspoons kosher salt 1 teaspoon Tabasco 1/2 teaspoon freshly ground pepper One 8-pound seedless watermelon, scooped into balls with a melon baller or cut into 1 1/2-inch chunks (10 cups), chilled 1/2 pound feta cheese, crumbled (2 cups) 1 1/4 cups pitted kalamata olives, coarsely chopped (optional) 1 small sweet onion, cut into 1/2-inch dice 1 cup coarsely chopped mint leaves