Add the chicken, 1 chopped onion, garlic, beer, green chilis, taco seasoning and juice of one lime into a slow cooker. Cook on low for 6-8 hours or on high for 4-5 hours. Shred chicken.
Once chicken is cooked, preheat broiler and place rack at top. Grease large baking sheet with cooking spray. Using slotted spoon, transfer shredded chicken to baking sheet and spread throughout in even layer. Place under broiler for about 5 minutes or until edges start to brown. Remove from oven and add ⅓ cup of leftover juice from slow cooker. Broil for additional 5 minutes. Remove again and add ⅓ cup of juice and broil again for 5 minutes.
For tortillas, heat small skillet over medium heat and cook for 30 seconds on both side. Serve chicken over warm tortillas with desired toppings.
Notes
While you can throw frozen chicken in the slow cooker, but I recommend thawing it first before cooking.
You can replace the beer with chicken stock or even salsa.
To make the corn tortillas pliable, heat a small skillet over medium heat and cook for 30 seconds on each side. You can also cover the tortillas with a wet paper towel and place in the microwave for 30 seconds.
Don't skip on toppings like avocado, cheese, cilantro and tomatoes.