Ingredients
2 lbs boneless skinless chicken breasts (about 4-5 chicken breasts) or flank steak
1 onion, thinly sliced (I use red onion)
1 red bell pepper, sliced in half-circle slices
1 green bell pepper, sliced in half-circle slices
2 teaspoons chili powder
1 teaspoon ground cumin
1/4 teaspoon salt
1/2 cup chicken broth (I used homemade chicken stock)
2 tablespoons fresh lime juice (or more, I use about 3 T)

For Serving:
flour tortillas 
grated cheese
sour cream
guacamole 
salsa

Directions

1. Trim all visible fat and tendons from chicken breasts, and cut chicken into 1 inch crosswise slices. Place chicken in crockpot.
2. Cut both ends from onion, then peel, cut in half top to botton, and cut into half-circle slices. Add onion to crockpot. Cut ends from red and green bell pepper, cut in half top to bottom, remove seeds and membranes, and cut into half-circle slices. (Cut up the stem and bottom end too.) Add bell peppers to crockpot.
3. Squeeze lime juice over chicken, onions, and peppers in crockpot. In a small bowl stir chili powder, cumin and salt into chicken broth. Pour over chicken. Cover and cook on low for 6-7 hours or on high for 3-4 hours, or until tender. (I usually cook about 3 hours on high.)
4. Spoon chicken and vegetables into warmed tortillas and serve with toppings. This is also delicious just served on a plate, with cheese melted over and other toppings added.