Heat the olive oil in a deep-sided skillet over medium-low heat. Cook the onions until transparent, then add the garlic, cooking for 30 seconds longer. Add the ground beef and 1 teaspoon of fish sauce, and cook until the beef is no longer pink. Stir in the sweet potato and cook until the sweet potato is just starting to soften.
Add the carrots, bean sprouts and cabbage to the pan. Cook until the cabbage wilts, about 4 minutes. Stir in the green beans, season with remaining fish sauce and pepper, to taste. Give it a little drizzle of olive oil to finish.
Make the dressing by stirring the garlic, vinegar, and pepper in a small bowl. Serve with rice, and drizzle with garlic vinegar dressing.