Cucumber-stuffed Tomatoes

Cut the white part of the onions lengthwise, then slice the white and green parts finely. Place in a glass or plastic bowl. Add vinegar, olive oil and seasonings and mix well. Wash and core the tomatoes. With a serrated knife, cut a thin slice off the top. Cut into the middle, around the inside, being careful not to get too close to the shell. With a teaspoon, scoop out the seeds and ribs inside the tomato, leaving a thin shell of flesh and skin. Turn upside down on a paper towel to drain. Place the insides in a plastic colander or strainer to drain. Peel the cucumber. Cut lengthwise, and scoop out most of the seeds. Chop or cube finely. Do NOT liquefy in a food processor or blender! Add to the onion mixture and stir. Press on the tomato remnants in the colander to remove most of the moisture. Turn out onto a cutting board and chop. Add to the onion and cucumber mixture and mix gently. When ready to serve, fill the four tomato shells completely with the cucumber mixture. Make nests of torn lettuce leaves in individual salad bowls, then nestle a tomato in each bowl. Drain and spoon any leftover cucumber mixture onto the lettuce leaves, around the outside of the tomatoes. Serve with steak knives for ease in eating. For more, see http://sneakykitchen.com/Recipes/cucumber_stuffed_tomatoes.htm