Bring pot of water to boil for pasta.
Fry onion and garlic in oil until soft.
Add chicken breast, cook until brown.
Heat chicken stock and milk until hot, not boiling.
Add pasta to water and simmer.
Add chorizo to chicken and onions.
Whisk corn flour in to stock/milk mixture, do not stop mixing until it has thickened. Remove from heat.
Drain cooked pasta, then mix with the chicken and chorizo, stir in the sauce.
Mix in the parmigiano just before serving.