Preparation Whisk together lemon zest, juice, mustard, salt, and pepper in a small bowl until smooth, then add oil in a stream, whisking until emulsified. Tear enough cabbage leaves from ribs into bite-size pieces to measure 7 cups, reserving thick ribs and remaining leaves for another use. Quarter avocado lengthwise, then pit and peel. Cut into 1/2-inch pieces. Toss cabbage leaves, avocado, and tomatoes in a large bowl with just enough dressing to coat.