Cut the cucumber in half & remove the seeds with a spoon. Then slice thinly.
Quarter the tomatoes and remove the seeds with a spoon. Then slice thinly.
Very thinly slice the red onion.
Whisk together the olive oil & vinegar & toss with the veg. Season w/ salt & fresh ground pepper.
If you have any fresh herbs, they would be awesome in here, 1-2tsp chopped fresh dill, basil, parsley, mint, etc.