PREPARATION:

1. Preheat oven to 400°F. Spray jelly-roll pan with nonstick cooking spray.
2. Scrub potatoes; pat dry. Cut potatoes into 1/2-inch cubes. Place on prepared pan; coat potatoes with cooking spray. Arrange in a single layer. Bake 20 to 25 minutes or until potatoes are tender and lightly browned, stirring occasionally.
3. While the potatoes are baking, combine oil, orange juice, lemon juice, mustard, salt and pepper in small bowl. Whisk until well blended.
4. Place potatoes in large bowl; cool slightly. Add tuna, tomatoes, green onions and oil mixture; toss gently to coat. Cover and chill at least 1 hour or up to 24 hours.
5. Let salad stand at room temperature 10 minutes. Toss gently and serve on lettuce leaves.