Make the vinaigrette. Add 5 tablespoons fresh-squeezed orange juice, 3 tablespoons olive oil, 1/4 cup red wine vinegar, 1 tablespoon Meyer lemon juice or fresh-squeezed lemon juice, 1 tablespoon whole-grain mustard, 2 minced garlic cloves, 1 teaspoon kosher salt, and 1/2 teaspoon black pepper to a pint-sized glass jar with a tight-fitting lid. Seal tightly and shake vigorously until well combined.
Assemble the salad. Add 2 1/2 cups diced cooked chicken, 2 cups baby spinach, 2 cups torn romaine or escarole leaves, 2 diced celery stalks, 1 (15-ounce) can drained and rinsed cannellini or white beans, 1 cup coarsely chopped chives, 1 diced small zucchini, and 1/3 cup chopped, drained, oil-packed sun-dried tomatoes to a large bowl. Toss gently to combine.
Dress and serve. Drizzle about one-third of the citrus vinaigrette over the salad and toss well. Add more vinaigrette if desired, then season with salt and ground black pepper to taste. Serve immediately. Refrigerate any remaining vinaigrette for up to 4 days and shake again before using.