In a small bowl, whisk 1/3 cup oil, vinegar and seasonings. Set aside.
Brush the onions, tomatoes, cucumber and romaine with remaining oil. Grill the onions, tomatoes and cucumber, uncovered, over medium heat for 4-5 minutes on each side or until onions are crisp-tender. Grill romaine for 30 seconds on each side or until heated through.
Chop the vegetables; place in a large bowl. Whisk dressing and pour over salad; toss to coat. Serve immediately.