In a large bowl, combine the chopped romaine lettuce, shredded red cabbage, shredded carrots, halved cherry tomatoes, diced cucumber, sliced green onions, and diced avocado.

In a separate bowl, whisk together the olive oil, red wine vinegar, Dijon mustard, minced garlic, sugar, salt, and black pepper until well combined.

Pour the dressing over the salad and toss gently to combine. Serve immediately.