In a small bowl, combine the dried cranberries with 3 Tbsp apple cider vinegar. Set aside so the cranberries can plump up while you're preparing the rest of the salad.
In a small pan over medium heat, toast the sunflower seeds. Toss frequently until they're lightly golden and fragrant.
Prepare the kale: Give it a good rinse, then pat dry and de-stem the leaves. You can cut the thick stems out with a sharp knife, or hold the base of the stem in one hand and pull the leaf from it with the other. Stack the de-stemmed leaves on top of one another, and using a very sharp knife, slice them into very thin ribbons. Place into a large bowl.
Drain the cranberries, reserving the liquid to use in the dressing.
In a small bowl whisk together 1 1/2 Tbsp apple cider vinegar (drained from the cranberries), olive oil, grainy mustard, smooth Dijon mustard, salt, and pepper.
Place the kale ribbons in a large bowl. Add a little bit of dressing and use your fingers to massage it into the kale until tender, approximately 30 seconds.
Add the with sunflower seeds, cranberries, smoked feta, dill, green onions, and quinoa (if using). Pour the remaining dressing over the salad, and give everything a good toss.
Let the salad stand for about 10 minutes before serving - a longer stint in the fridge is perfectly fine.