- Combine first 4 ingredients in a large bowl, stirring with a whisk.
- Gradually add olive oil, stirring constantly with a whisk.
- Add onion, cilantro, and coleslaw.
- Cut jalapeno in half crosswise, discarding the top. Remove seeds. Cut into thin rings/slices or finely dice.
- Add the jalapeños to onion mixture, and toss well to coat.
- Cover and chill at least 1 hour.