Same ratio of cucumber and tomato. A little less onion, small hand of parsley. start off with 1/2 a lemon squeezed. Pour olive oil to taste. Let it marinate for 5 minutes at least.
Remember not to let it sit for too long since vegetable oils go rancid very quickly. Ideally, buy extra virgin cold pressed olive oil is a amber glass jar. So the light does and oxygen do not make the fats go rancid. Fats go rancid way before you can even tell since they are barely any amino acids. Same goes for coconut oil, etc.