Slow Cooker Tortilla Soup

Name: Slow Cooker Tortilla Soup
Ingredients: 2.5 lbs chicken breasts or thighs, skinless and boneless; 1 large onion, diced (about 2 cups); 1 green bell pepper, diced (about 1 cup); 1 red bell pepper, diced (about 1 cup); 1 (28 oz) can diced tomatoes; 1 (15 oz) can black beans, rinsed and drained; 1 (15 oz) can corn; 1½ qts chicken stock (make sure it is gluten-free if need be); ¼ cup chopped fresh cilantro; 1 tbsp cumin; 1 tbsp chili powder; ½ tsp cayenne pepper; 1 tsp salt; 1 tsp garlic powder; 1 lime, juiced; 5 corn tortillas; avocado (for serving)