Preheat oven to 450 degrees F (230 degrees C). Line a baking sheet with aluminum foil and spray with cooking spray.
Combine corn flakes and walnut pieces in a gallon-size resealable bag; press air out and seal. Crush corn flakes and walnuts using a rolling pin until cereal is finely crushed and walnuts are the size of rice. Add garlic powder, salt, and pepper; shake bag to mix.
Dip chicken tenders in the egg to coat, allowing excess egg to drip back into bowl. Transfer chicken to corn flake mixture, 1 at a time, and gently shake until chicken is coated. Arrange coated chicken on the prepared baking sheet.
Bake in the preheated oven until chicken is cooked through and coating is lightly browned, about 10 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).