Peel garlic, and using a garlic press, add garlic to vinegar and allow to sit at least 10 minutes. (Alternatively, if you don't have a garlic press, mince garlic finely and then sprinkle with salt and rub the side of your knife across it to crush garlic to a fine paste, then add to vinegar as above.) Stir pepper, oregano, basil, and red pepper flakes into vinegar. Add chopped onion, stir to mix together.
Wash and thoroughly dry the escarole and separate the leaves, tearing them into 1-2 inch pieces. Add to vinegar and garlic, chop the cucumber into one inch pieces and season with black pepper.
If using the optional anchovies, break them into sections and add to the olive oil. Otherwise, pour olive oil over salad, sprinkle with salt and mix gently but thoroughly. Taste and adjust seasonings.
Escarole salad can be easily varied to suit the ingredients that you have available, or what's seasonal at the market. But remember, it's best kept rather simple, with not too many ingredients.
This can be topped with Parmesan croutons or served with [bruschetta]. When in season, optionally add fresh ripe tomato slices and use chopped fresh basil and oregano. Another nice addition is roasted red peppers. Or add 2" X 1/2" slices of salami, mortadella or a sharp Italian cheese such as Asiago or Provolone. Or add a can of cannelloni beans (drained), or a can of Italian Tonno (tuna) packed in olive oil.
Note: When using anchovies, adjust salt, as anchovies can be very salty depending on how they're packed.