I have found a lovely thick natural Greek yogurt but if yours is runny then I would suggest draining it before adding to the recipe. Simply place a fine sieve over a large enough bowl, add a cheesecloth or similar and pour the yogurt in. Cover and whack into the fridge overnight and in the morning your will have a lovely thick yogurt in the sieve.
When ready to produce the tzatziki, peel the cucumbers and throw away the skin. Slice the cucumber in half lengthways and using a spoon scoop out the seeds.
1 large cucumber
Place a box grater over a kitchen towel and grate the cucumber so the pieces fall onto the towel.
Add a pinch of salt and fold the corner over and place the towel in a large dish to remove the excess water. When ready squeeze the towel to drain the last of the fluid. This helps to prevent a runny Tzatziki.
Once drained place the cucumber into a food processor along with the garlic, olive oil, lemon juice, salt, pepper and Greek yogurt. Blitz until lovely and smooth.
16 oz Greek yogurt, 2 cloves garlic, 1 large lemon, 2 tbsp olive oil, 1 tbsp dill, salt, ground black pepper
Transfer to a serving bowl and place in the fridge for at least an hour so the flavour become enhanced.