In a large bowl, toss to combine the kale and romaine.
Top with the red onion and avocado. TO MAKE THE DRESSING In a small bowl, whisk together the balsamic vinegar, Dijon mustard, and honey.
While whisking, drizzle in the olive oil.
Season with salt and pepper.
Pour the dressing over the salad and toss well, making sure all the kale has been coated, and serve. VARIATION 1 CHICKEN-KALE SALAD WITH ONION AND AVOCADO: Add 6 to 8 ounces diced or shredded cooked chicken breast to this salad to make it more of a main dish. (You might want to add another teaspoon or two of dressing.) VARIATION 2 SPINACH-KALE SALAD WITH ONION AND SALMON: Add a couple of handfuls of well-washed and drained spinach leaves to the salad, and top with 6 to 8 ounces cooked salmon. (You don’t need to massage the already-tender spinach.) PREP TIP: Make the salad ahead of time and dress right before serving.