Whisk all dressing ingredients together in a measuring cup or small bowl.
Mix all vegetables together in a large mixing bowl and toss with dressing to coat. Cover and chill for 30 minutes up to 3 hours. Add sunflower seeds and any salt if necessary before serving.
Notes
Store leftovers in an airtight container in the refrigerator. The slaw will be less crisp the next day, so it tastes best when served the same day.