This is a great side salad with your picnic foods like hot dogs and hamburgers, or a more formal setting of chicken and rice.
Cut cucumber (and large tomato) in half. Remove seeds. Chop cucumber, tomatoes, bell pepper and onion. If using heirloom tomatoes, cut them into fourths.
Whisk together oil and next 4 ingredients in a large bowl until sugar dissolves. Add cucumber mixture, tossing to coat. Cover and chill 3 hours before serving.