Preheat your oven to 350 degrees F. Spread the pecans on an ungreased baking sheet in a single layer. Bake for 5-10 minutes, tossing once or twice throughout, until toasted and fragrant. Watch carefully and set a timer so that the nuts do not burn. Remove from the baking sheet and set aside.
Slice the onion thinly and place in a small bowl. Cover with cold tap water and set aside for 10 minutes while you finish preparing the rest of the salad (this will keep the onion's flavor but prevent the onion from having such a harsh, raw bite.) Drain the onion and lightly pat dry.
Slice the pomegranate in half across its "equator" (NOT top to bottom). Working one half at a time, turn the pomegranate over an empty bowl, cut side down, and squeeze it gently all the way around to loosen the seeds. With the back of a wooden spoon, firmly wrap the back of the pomegranate, knocking the seeds into the bowl (be careful—the juice can splatter). Rotate the pomegranate then repeat, so that you tap it all the way around and knock out as many seeds as possible. Slice the pomegranate into big wedges and remove any seeds you missed with your fingers. Repeat with the second half. Measure out 1/2 cup of the seeds for the recipe, then save the rest for a different use.
In a small bowl or large measuring cup, whisk together all of the dressing ingredients: olive oil, apple cider vinegar, mustard, honey, salt, and pepper. Alternatively, you can shake all of the ingredients together in a tightly sealed mason jar.
Place the kale and onion slices in a large serving bowl. Pour the dressing over the top. Toss to coat, then let the salad rest in the refrigerator for 20 minutes if time allows (the flavors will meld and the kale will become more tender). Just before serving, sprinkle with the toasted pecans, pomegranate seeds, feta, and parsley. Toss lightly and serve.
TO MAKE AHEAD: Winter salad can be made up to 8 hours in advance (including adding the dressing—in fact, it will be better if you do!). Store in the refrigerator until ready to serve, or set out up to 1 hour in advance.