Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
     2/3  cup           olive oil
     1/3  cup           wine vinegar
   1      teaspoon      salt
     1/4  teaspoon      pepper
   1      clove         garlic -- crushed
   1      teaspoon      dried oregano leaves
   1                    lemon -- juice of
   1      medium        onion -- thinly sliced and
                        -- separated into
                        rings
   2      pounds        shrimp -- cooked, peeled,
                        -- deveined
                        cherry tomatoes -- optional
                        endive -- optional
                        fresh mushrooms -- optional

Preparation:

Combine first 8 ingredients in a medium mixing bowl; stir well. Add shrimp; toss. Cover tightly and refrigerate 2 hours, tossing occasionally. Drain shrimp. Pour shrimp into a serving bowl; garnish with cherry tomatoes, endive and mushrooms, if desired.