Set the oven to 220 Degrees C.
Add the olive oil to a shallow frying pan, then sear the chicken to seal the meat. Add the onions and carrots towards the end to lightly fry those.
Add the chicken and vegetables to the casserole dish. Top with the chicken casserole mix and stock pot. Fill the dish to almost three quarters of the level of contents, stir, then cover the dish with a lid, or tin foil.
Reduce the heat of the oven to 180 Degree C and cook for up to 2 hours, or the chicken and vegetables are fully cooked.
If you prefer a thicker gravy, remove the casserole from the dish about ten to twenty minutes before the end of cooking. Mix cornflour with a little water until it is fully dissolved. Add it to the dish and fold into the casserole. Put the casserole back in the oven until the gravy has thickened.