Slice tomatoes and place on platter. Slice onions, separate into rings and place on top of tomatoes.
Cut corn off cob and sprinkle over tomatoes and onions. Tear basil into small pieces and place on top of corn.
In a small bowl or jar, combine lemon juice, olive oil, salt and pepper. Mix together. Pour dressing over salad. Sprinkle with additional salt and pepper. Serve immediately.