- Pat chicken dry with paper towels and season with salt and pepper.
- In a large heavy pot, heat oil over medium-high. Add chicken and cook, stirring occasionally, 5 minutes.
- Add onion, cumin, and chile, if using, and cook 3 minutes.
- Add tomatillos and 1 cup water, scraping up any browned bits with a wooden spoon; season with salt and pepper. Bring to a rapid simmer and cook, stirring occasionally, until mixture is thick and meat can be shredded with a fork, 25 minutes (add up to 1/2 cup more water, if necessary).
- Shred chicken, add cilantro, and season with salt and pepper. Serve chicken mixture in taco shells with Monterey Jack and lettuce.
Source: http://www.marthastewart.com/903162/tacos-tangy-cilantro-chicken#recipe-content