A good way to avoid the hassle of peeling and chopping potatoes is to bake them in the oven. While baking takes longer than boiling, it can be done with the skins on.
Scrub the spuds until there is no dirt on them, and then poke a few holes in each one to allow the steam to escape. Bake in the oven for 50 minutes to an hour at 425 Fahrenheit.
When baking the potatoes, you won't have to watch the pot to ensure it doesn't boil over, so you can do something else, like dicing and cooking your onions.
Cut the baked potatoes in half length-wise and scoop the insides into your slow cooker or soup pot. There's no need to mash them as they will be fall-apart soft.