Slow Cooker Chicken Casserole

This casserole includes browning the chicken and sauteing vegetables before adding to the slow cooker. Technically these steps are not necessary but doing so results in a mellower, more balanced casserole with a slightly sweeter flavour. For this reason, I choose to brown beforehand. 
However, I do think you have to weigh up your priorities. Although browning makes a difference in taste you may feel that dirtying a pan and the extra time required is not actually worth that difference. In that case, you can just chop, dump everything in the pot, set it to cook and go!
If you do choose to skip the browning then omit the oil and vinegar and whisk the flour with the chicken stock before adding to the slow cooker.

The chicken you use is personal preference, see notes below.
Chicken Thigh  (Skin on vs skin off) - If you are pre-cooking then using skin-on thighs will produce added flavour, make sure to sear them well. Add chicken skin-side down to the hot oil, cook until skin is golden in colour, around 5 minutes. If you choose to skip the searing stage then I would recommend removing the skins as they can go a funny texture if added raw to the slow cooker.  Chicken Thigh (Bone in vs Boneless) - I didn't find a big difference in texture or flavour when using bone-in or boneless thighs in this dish. For younger children it might be easier to use boneless, my youngest certainly preferred it without the bones.  
Chicken Breast - If using chicken breasts I recommend adding them whole rather than chopping them into pieces. They will fall apart easily and I suggest shredding the chicken (like in this slow cooker chicken curry). It will give a different feel to the dish but will still be delicious.

To thicken; in a small bowl, whisk together 2 tablespoon of flour/cornflour with ½ cup of the casserole broth. Stir the flour mixture into the slow cooker. Cover and cook on high heat for an additional 30 minutes, or until thickened.

Refrigerate: Allow the casserole to cool; store in an airtight container and refrigerate for up to 3 days.
Reheat on the stovetop or microwave.
Freeze: Allow the casserole to cool, transfer to an airtight container and freeze for up to 3 months.
If I am making purposely to freeze, I often cook it without potatoes and instead serve with mashed potatoes. Although it is perfectly safe to freeze potatoes, I sometimes find the texture changes and they can become a little soft and grainy.
Thaw, overnight, in a refrigerator, and reheat on the stovetop or microwave.