Store 12 cups mixed hearty greens (such as escarole, mustard greens, and kale; if using mustard greens or kale, fold leaves over and cut off tough center rib and stems) and 1 cup kumquats, cut into thin rounds, seeded, in 2 separate resealable plastic bags. Chill greens and kumquats overnight. Before serving, empty bags with greens and kumquats into a large bowl. Add 1/2 cup Granny Smith Apple Cider Vinaigrette to salad and toss to evenly coat.
Add more vinaigrette, if desired. Season to taste with kosher salt and freshly ground black pepper. Transfer to a serving bowl and scatter 1/4 cup 1" pieces chives and, for a little crunch, 3 tablespoons roasted salted shelled pumpkin seeds (pepitas) over.
