In a medium bowl, whisk together Greek yogurt, dill, mayonnaise, Dijon mustard, lime juice, lime zest, black pepper, salt and chili flakes (if using) until smooth.
½ cup Greek yogurt, 3 tablespoons fresh dill, 2 tablespoons mayonnaise, 1 tablespoon Dijon mustard, 1 tablespoon lime juice, 1 teaspoon lime zest, ½ teaspoon black pepper, ½ teaspoon fine sea salt, ¼ teaspoon dried chili flakes