Put the chicken, ginger, lemongrass and coconut milk in a pan and bring to a simmer. Add a pinch of salt, then reduce the heat and cook for 10-15 mins until the chicken is cooked through. Cool, then chill until cold.
Cook the noodles following pack instructions. Lift the chicken out of the coconut liquid and shred it, then stir the peanut butter into enough of the liquid to make a thick dressing.
Divide the noodles between four jars or boxes and spoon over the coconut dressing, or take it with you in a separate jar. Add the beans and tomatoes followed by the chicken and spinach. Seal the lid and chill the jars until you need to pack them. Serve in the jar or, for smaller children tip into bowls.