Add the eggnog, oats, and chia seeds to a large jar, seal with the lid, and shake until well combined. Refrigerate overnight, or at least 4 hours. (Note: if you're able to stir the oats a few times during the refrigeration period, do so!).
Stir well before serving the oats in bowls. Drizzle with additional maple syrup to sweeten (skip this if you're using store-bought or already very sweet eggnog), sprinkle with ground cinnamon and freshly grated nutmeg, and top with dried cranberries, pumpkin seeds, and chopped pecans.