Cut up the chicken in pieces. Put into a kettle with water (you may brown the chicken first if you wish). Add tomatoes and onion. Allow it to boil 30 minutes; add salt and oregano. If the chicken is tender, remove it with a little broth.
Prepare the bori by making a circle with the corn flour. In the center, add cheese, egg, and grease from chicken broth. Mix until you obtain a dough. Roll the dough with your hands and make little balls. Add balls to the boiling broth.
When balls float to the surface, allow it to boil for a few more minutes. Add the pieces of chicken, whole. Serve hot.