Deseed, and then slice the cucumber into thin slices, and press to remove all juices (use a tofu press, or press in a strainer or juice bag). Set aside (optionally place in paper towels to remove more liquid).
Add tofu, garlic, lemon juice and zest, vinegars, onion powder, salt and pepper to a high speed blender or food processor and blend until smooth.
Add the dill, parsley, and mint and pulse until the herbs are small flakes in the spread.
Add cucumber to blender and pulse a few times to incorporate well.
Add more lemon juice as needed.
Thin with water or plant-based milk as desired.
Sub with other tofu types, such as silken or medium firmness for different consistencies.
This will be thick before adding the cucumber - you may need to scrape down the sides. If you want a very thick tzatziki, use a food processor to blend and ensure you deseed and really dry the cucumber out well.
This makes about 18oz (500g) of Tzatziki.