I found this at Daiso, the $2 supermart:
Japanese Seasoning for pickled cucumber in mustard :
It comes in 3 small packets in the bigger package on topmost picture.
Ingredients: mustard, glucose, salt, soy sauce, (soybean, wheat, salt, water), vinegar, kelp, turmeric, seasoning, Vit C, alnm, xtanthan, gum, enzyme
According to the drawings on the label, just pour the small packet into a bag of sliced cucumber (The Japanese type of cucumber is more recommended as it is more crunchy), tie it up and let it marinate by itself.
To better marinate it, I mixed it with some water , just about 2 tablespoon (Not too much water is to be mixed as the cucumber itself will release its own water content after sometime) and sealed it in those lunchboxes and put it into the fridge. After 2-3 hrs later, I have my lightly pickled cucumber.
It is quite a success as my mum loves it. It kind of tasted like wasabi sauce but much lighter than wasabi. A refreshing taste. :-)