Add the apple cider vinegar, soy sauce, water, brown sugar, garlic granules, onion granules, cinnamon, and pepper to a small pot.
Heat on medium-high, and bring to a boil, stirring frequently. Let it boil for 2 minutes, then lower to a simmer, and cook for 10 minutes.
Remove from the heat, and let it cool for 20 minutes. Serve, or store in the fridge for up to 3 weeks.
