1. Mix together all ingredients except the garlic mustard leaves, garlic, and peanut oil in a saucepan with a whisk, bring to a boil over medium heat, stirring constantly, reduce the heat to low, cover, and simmer 5 minutes stirring occassionally.
2. Meanwhile, heat the oil in a wok or skillet and stir-fry the garlic mustard and garlic 1.5 minutes, stirring constantly.
3. Pour the sauce over the garlic mustard mixture and cook over high heat 3 minutes or until the garlic mustard leaves are tender, stirring constantly.