Heat oil in large pan, add onion and carrot to soften, add chicken to slightly brown, mix in all other ingredients and transfer to slow cooker.
Cook on low for 4 hours(see note)
Line baking dish with puff pastry and transfer mixture. Place another sheet of puff pastry on top and cook in the oven at 180 degrees until pastry has turned a nice golden colour(roughly 20 minutes)
NOTE
I brown the chicken first because I think it gives it a nicer flavour. However, if you don't like browning first you can add in the raw chicken with the rest of the ingredients and cook on low for 8 hours.
If the mixture is too watery when cooked just use corn flour to thicken ??