Wash all veggies and dry thorougly. Cut everything except the olives and the spices into chunks, not slices (even the onions!). Toss together in your favorite salad bowl. Add the oregano and a couple of tablespoons each of the vinegar and olive oil and toss again. Serve at room temperature or slightly chilled.
Feel free to add or remove ingredients at will--just keep the proportion of tomatoes to other stuff pretty constant.