I love this very simple salad. It takes no time at all to pull it together, and it's delicious, with the crisp crunch of English cucumber and the biting tang of fresh tomatoes. There are two ways to dress this salad. My favorite method involves fragrant sesame oil and seasoned rice vinegar. Another good method is to add a bit of feta cheese and dress the ingredients with a light vinaigrette. Both are quick and easy to prepare, but have very distinctive flavors -- one with Asian notes, while the other has a Mediterranean flair (especially if you also add kalamata olives).
I like to use English cucumbers. They're the long ones wrapped in plastic. Their skins are thinner and less waxy, so they don't need to be peeled. They also have fewer seeds. Tomatoes fresh from the garden are best to use, but as an alternative firm, ripe tomatoes on the vine from the store are just fine. Sweet cherry tomatoes would work as well. This isn't a fussy recipe.
The brand of seasoned rice vinegar my mother likes to use in this recipe (I know it from her) is Marukan, so that's what I use, but I'm sure other seasoned rice vinegars would work as well. If you choose to use unseasoned rice vinegar, just know that you'll have to add your own sugar, salt, mirin, etc., in order to achieve the same flavor, otherwise it'll be rather bland.
Because of the tomatoes, this salad is best consumed the same day it's made. Refrigeration makes the tomatoes mealy and the whole salad becomes unpleasantly watery. Besides, the vegetables taste their best at room temperature.
I don't have a specific recipe, because there are so few ingredients and the amount of vegetables used as well as preference dictates the seasoning. Use more tomatoes, use fewer tomatoes. Add a little rice vinegar or add a lot. Use a whole cucumber or only use half. Drizzle the seasonings over the vegetables modestly, then taste it. If it needs more of anything, add it. Serve and enjoy -- I guarantee you will eat a lot more than you think you will!