1. For dressing, combine oil, orange juice, vinegar, honey, and pepper in a blender container or food processor bowl. Cover and blend or process until combined. Place in an airtight jar and refrigerate for at least 30 minutes.
2. Use a small sharp knife to peel grapefruit and oranges, removing as much of the white pith as possible. Section fruit and place in a large bowl. Add grapes and pomegranate seeds, if desired.
3. To serve, toss with dressing. Line a large bowl with torn lettuce and top with fruit mixture. Makes 12 servings.
Make-ahead tip: Refrigerate dressing up to 3 days. Store prepared fruit mixture, covered, in refrigerator up to 4 hours.