Place the chicken breasts in the slow cooker. Sprinkle them with garlic powder, paprika, and salt, then pour the buffalo sauce over the top.
Cover and cook on low for 6 hours or until the chicken shreds easily with two forks.
While the chicken cooks, make the avocado crema. Add the avocados, Greek yogurt, lime juice, cilantro, and cumin to a food processor or blender. Blend until smooth.
Warm the corn tortillas in a dry skillet over medium heat for about 30 seconds per side.
Shred the chicken directly in the slow cooker and stir it into the remaining sauce. Spoon the chicken into the warm tortillas and drizzle with avocado crema before serving.