Cook 2 chicken breasts according to your preference (baked, boiled, or grilled) until fully cooked. Once cooked through, shred and chop into bite-sized pieces. Set aside to cool.
While the chicken is cooling, chop 2 celery stalks and 2 green onions into small, manageable pieces.
In a large bowl, combine the shredded chicken, chopped celery, sliced green onions, 1/2 cup blackberries (sliced in half or quarters), and 1/4 cup chopped walnuts.
Stir in 1 cup cottage cheese and 1/4 cup mayonnaise to the mixture. Mix well until all ingredients are evenly combined.
Season the salad with 1/2 tsp salt and pepper to enhance the flavors. Adjust to taste as preferred.
Serve the salad as is or on your favorite keto bread for a hearty sandwich option.