In a medium saucepan cook rice with 1 tsp salt according to package directions and cool completely.
Bring a large saucepan of well-salted water to a boil. Add cauliflower and cook until just tender, about 5 minutes. Transfer to a colander with a slotted spoon and drain well. Add potatoes to boiling water and cook until just tender, 8-10 minutes. Transfer to the colander to drain.
In a blender combine avocado, herbs, oil, lemon juice, and ½ tsp salt. Add ⅓-½ cup water and blend until completely smooth.
In a large bowl, toss rice, cauliflower, potatoes, carrots, and cabbage. Drizzle with avocado dressing and serve.