For the green juice: Add the parsley, kale, lemon juice, ginger, celery, apples, cucumber and 1 cup water to a blender and blend until smooth. Strain through a cheesecloth or coffee filter-lined wire mesh strainer. (Green juice keeps, refrigerated in an airtight container, for up to 1 week.)
For the martini: Add the gin and 8 ounces green juice to a shaker filled with ice (save the remainder for another use). Shake vigorously and strain into 4 martini glasses. Add 2 dashes of your favorite bitters to each glass, if using.