Finely mince the cucumber. Place Greek yogurt, lemon juice, garlic, salt and dill (if using) in a smallish mixing bowl. Stir with a spoon until well combined. Stir in the minced cucumber. Serve or refrigerate immediately.
For a smooth tzatziki sauce, add all ingredients to a food processor or a blender (I like to use a smoothie cup attachment) and blend until smooth.
Video
Notes
Dill isn't technically a traditional tzatziki sauce ingredient, but is a very popular add-in. If you are a dill fan, feel free to stir in the dill or garnish the tzatziki with it.
Any type of cucumber is fine. For a regular cucumber, use about half. If you're using snack size cucumbers, around 2-3, depending on size.