Add the potato slices to boiling salted water and cook for 5 minutes then place them in a colander to drain and cool.
Spray the bottom of a large saucepan 5 times with the low calorie cooking spray. Turn the heat under the saucepan on high initially and when the oil begins to bubble a little turn the heat down and add the onion and mushrooms. Sauté them until they are soft. About 5 minutes.
Once the onion and mushrooms are softened add the cooked chicken, corn flour water mixture, skimmed milk and chicken stock. Stir everything together well until thickened and then season to taste.
Add the frozen sweetcorn, bring the whole mixture to the boil, then turn down the heat and allow everything to simmer gently for about 5 minutes.
Turn the bake mixture into an ovenproof dish and top the mixture with the potato slices.
Spray the top of the potatoes evenly with the low calorie cooking spray (about 6 – 8 sprays).
Bake in the centre of your oven for about 45 minutes until the potatoes are brown and crispy.
For the French Style Green Beans:-
Whilst the casserole is baking. Put 2 tbsp. of the hot vegetable stock into a saucepan along with the finely chopped garlic and turn on the heat allowing the garlic to cook a little in the hot stock for 3- 4 minutes.
Add the rest of the vegetable stock and then the green beans and simmer until cooked to preference.