Preheat oven to 375 degrees F (190 degrees C). Grease a baking sheet with the avocado oil. Place chicken on the baking sheet.
Bake in the preheated oven for 15 minutes. Cut chicken breast in half horizontally and top each half with tomato sauce, oregano, and mozzarella cheese.
Continue cooking until chicken is no longer pink in the center and the cheese is melted, about 15 minutes more. An instant-read thermometer inserted into the center of the chicken should read at least 165 degrees F (74 degrees C).
