Put your carrots, onions, celery, mushrooms, and zucchini, in large frying pan on medium with a bit of water. Cover and allow vegetables to steam until cooked.
Make the roux by combining the olive oil and flour in a pan over medium heat and whisk until smooth. Add the Dijon mustard into the roux and mix. Then, add the milk to the roux and mix until it thickens.
For your sweet potato topping, cut up your cooked potatoes and place into a blender with the oats and the eggs. Blend until texture is smooth.
Put your cooked vegetables into a deep baking dish, and then add the pre-cooked chicken, roux, and some sliced parsley. Lastly, spread the sweet potato topping on top of everything, pop into the oven, and bake for 30 minutes!