1. Shred jicama on large holes of a box grater. Working with a handful at a time, squeeze out excess moisture. Transfer jicama to a large bowl (you should have about 3 cups) and toss with lemon juice. Add bell peppers, carrots and cabbage and toss again.
2. In a small bowl, whisk together vinegar, mustard, sugar and oil until emulsified. Season with salt and pepper. Pour half of dressing over slaw, add cilantro and toss well. Add more dressing, if desired, and toss again. Serve immediately.