To make vinaigrette:
Add all ingredients to a jar, close tightly, and shake vigorously. (I like mine tart with only 1/4 cup olive oil. Add 1/3 cup if you prefer a milder vinaigrette.) Alternatively, you add all ingredients except oil to your blender or whisk in a bowl. Slowly add oil until emulsified. Makes approximately 1/2 cup. *(Half this recipe if you want a very lightly dressed salad and don’t want any leftover vinaigrette for other uses.)
To make salad:
Slice your onions (very thinly) and cucumbers and pour about 1/4 cup of vinaigrette over them. Toss to coat and allow to sit for at least 5 minutes. Let this marinate while you are chopping everything else (or make this part ahead of time and add the rest before serving). Chop the tomatoes (discarding most of the seeds and juice) and chop or chiffonade the basil. Add to salad and mix thoroughly. Add more of the vinaigrette to preference (you may not want to add all of it), reserving some for the table if you’d like. Optional: mixed in some chopped avocado and top with feta or goat or other cheese before serving.