Prepare the vegetables by shredding the green and red cabbage finely. Slice the cucumbers and onions, and grate the carrot.
Place all the chopped vegetables in a large mixing bowl. Sprinkle with salt and massage gently with your hands for 1 minute to slightly soften the cabbage and release natural juices.
In a small pan, heat the olive oil over medium heat. Once hot, add the mustard seeds. Let them sizzle and pop for about 30 seconds to release their aroma.
Immediately pour the hot oil and mustard seeds over the salad mixture.
Add the lemon juice and grated ginger (if using). Toss everything thoroughly to combine.
Let the salad sit for 10-15 minutes before serving to allow the flavors to meld. Serve as a light dinner or a healthy side dish.