Place the cabbage and carrots in a large heat-proof bowl. Pour the boiling water into the bowl to cover the cabbage and carrots and set aside for about 5 minutes. Drain in a colander, pressing out as much liquid as possible.
Return the cabbage to the bowl and toss with the remaining of the ingredients. Let set at room temperature for a couple hours if you like. Then chill and serve as an accompaniment to pupusas or as a side dish.