Cook the couscous according to the package directions.
Meanwhile, heat the oil in a large skillet over medium-low heat. Add the garlic and cook for 1 1/2 minutes. Add the sugar, nutmeg, vinegar, and orange juice and bring to a simmer. Add the peaches and continue to simmer until the liquid has reduced slightly, about 5 minutes.
Divide the couscous and chicken among individual bowls, top with the peach sauce, and sprinkle with the parsley (if using).