Place broth, orange juice concentrate, chipotle, adobo, and garlic in a blender or food processor. Blend until smooth.
Place chicken in a 4-qt. or larger slow cooker and season with salt. Pour the sauce over the chicken. Cover and cook on Low until the chicken is tender and can easily be pulled apart with a fork, 4 to 5 hours.
Transfer the chicken to a cutting board. Let cool slightly.
Carefully transfer the cooking liquid to a medium saucepan. Bring to a boil over medium-high heat. Cook until reduced to 3/4 cup, about 15 minutes. Return the sauce to the slow cooker.
Meanwhile, prepare salsa: Zest orange, then peel; chop the segments. Mix onion, cilantro, lime juice, the orange zest, and the chopped orange in a medium bowl. Add avocado and toss gently until just combined.
Using 2 forks, shred the chicken. Return it to the slow cooker and stir to combine with the sauce. To serve, divide the chicken among tortillas and top with cabbage and the salsa.
Equipment: 4-qt. or larger slow cooker