Strain the Greek yogurt using a fine mesh strainer or coffee filter for a few hours to remove excess liquid.
Peel and seed the cucumber, then grate it or finely chop it.
Place the cucumber in a strainer, sprinkle lightly with salt, and squeeze out as much liquid as possible.
In a bowl, combine strained yogurt, cucumber, garlic, lemon juice, dill, and chives.
Season with salt and pepper to taste.
Mix until smooth and well combined.
Refrigerate for at least 1 hour before serving to allow flavors to develop. This Tzatziki Sauce is best served chilled.