Storage: The sauce can be stored in a glass jar in the refrigerator for up to 1 week. It may separate; simply stir before using.
Substitutions: If you don't have French mustard, regular Dijon works well. For a gluten-free version, use tamari instead of soy sauce.
Variations: Add a dash of chili sauce for heat, or a spoonful of peanut butter for a satay-style twist.
Freezing: The stir-fry freezes well without the rice. Reheat gently in a pan, adding a splash of water if needed.