如果你想让留学生妈妈帮你做饭，你可以尝试以下表达：

1. "Mom, could you help me cook the meal before lunch？"

2. "I was wondering if you could assist me in preparing the meal for lunch？"

3. "Would it be possible for you to help me with cooking the meal today？"

这些表达都表示你希望妈妈在午餐前帮你做饭，语气礼貌且直接。你可以根据你们的习惯和舒适度选择合适的表达方式。