This makes a bunch of chicken, so freeze leftovers in 2 cup portions. The only variation I did was substitute a mexican spice mix called adobo for the cumin and oregano since it has both in it. I have also prepared it (accidentally) without the lime juice and it tastes fine. It is also good without the cilantro, but I LOVE cilantro, so I usually add some.
Place chicken in 4-quart slow cooker that has been lightly coated with no-stick cooking spray. In small bowl, stir together tomatoes, garlic and seasonings. Pour over chicken. Cook until chicken is tender, about 6 to 8 hours on low heat or 4 to 5 hours on high heat.
Remove chicken; cover and let stand 5 minutes. Use two forks to shred chicken. Return shredded chicken along with any accumulated juices to slow cooke; stir to combine. Stir in lime juice and cilantro. Serve with tortillas and your favorite taco toppings.