Peel and cube the sweet potatoes, then boil them until tender, about 5–10 minutes.

Cool the sweet potatoes in a colander to ensure they don't become soggy.

Combine the cooled sweet potatoes with celery, red onion, sunflower seeds, and cranberries in a large bowl.

Whisk together vegan mayo, optional mustard, salt, and pepper in a separate bowl.

Pour the dressing over the salad mixture and gently fold until well-coated.

Chill in the refrigerator for at least 30 minutes before serving.