Step 1

Combine drained black beans and diced tomatoes (with their liquid) in a slow cooker. Season with oregano, 1 1/2 tsp cumin, and 1 1/2 tsp chili powder.

Step 2

Pat chicken breast dry and season on all sides with salt, garlic powder, remaining 1 1/2 tsp cumin, and remaining 1 1/2 tsp chili powder. Place on top of bean mixture. Cover and cook on high 2 hours.

Step 3

Meanwhile, combine cabbage and vinegar in a bowl. Season with salt and set aside.

Step 4

At mealtime, preheat oven to 350°F (180°C). Drape tortillas across two wires of an oven rack and bake until crispy, about 8 minutes.

Step 5

Remove chicken breast from slow cooker and shred into bite-size pieces. Stir shredded chicken back into bean mixture; season with salt and pepper to taste.

Step 6

Slice avocados. Fill tacos with chicken mixture and top with cabbage and avocado.