One way for cucumbers is peel, slice thin, slide some red onions thin, sprinkle with dried or fresh dill, add vinegar and let sit a while.
Cucumber-feta salsa - from Whole Foods - 1 large cucumber peeled and roughly chopped; 1/3 cup red onion diced, 1/4 cup chopped fresh parsley,1 cup crumbled feta cheese, lemon zest, 1 tbsp lemon juice and one tbsp of olive oil, salt to taste. Finely chop cucumber in food processor, put in bowl and add everything else, stir it up. It says serve at room temperature, but we eat it cold out of the frig. I sometimes use more cucumbers and onion, but not more of everything else and seems to work. This is our new favorite.