America’s Test Kitchen gets it right in their “Slow-Cooker Revolution” book. Avoid putting chicken in a slow-cooker- but if you have to, cook it on low for no more than 4 hours. Chicken breast cooks in an oven between 25-40 minutes so what are you even doing? When I first got a slow-cooker eighty billion years ago (ok maybe 12 years ago…), I think there was a misunderstanding that you couldn’t cook anything on low for less than 6 hours. If you were cooking for only 4 hours, it had to be on high, no matter what. There were other misunderstandings like pasta and rice could be thrown in with the rest of the ingredients and not turn into chicken pudding for dinner time.** Or that vegetables would maintain their color after cooking for hours in brown liquid. Or that anything “slow-cooked” would have a delicious melt-in-your-mouth quality. Or that slow-cookers are for busy people (and require little to no prep/planning).
Anyway- I found a yellow curry chicken recipe for this weekend and I was happy to see it recommending 4-5 hours of cooking on low. But it also recommended putting in bell peppers and letting them cook that whole time. I knew a little better and put them in for the last hour. That’s also too long… they totally disintegrated. 
I still ended up with an Instagram-worthyish bowl… but look at those sad pepper bits… poor things.
The only vegetables that belong in a slow-cooker are anything you’d leave on a stove forever in a soup- onions, carrots, celery, potatoes. Anything else is lies (including already-cooked canned beans in chili- that is wrong!!!) Unless you stick it in for the last 15-30 minutes or so- but you’re using a slow-cooker bc you’re out doing important things so who has time for that?
Anyway- there are as many crappy slow-cooker recipes on the internet as there are cat videos. I feel the need to put it out there- slow-cookers can turn the crunchiest carrots into almost-purée so think twice before putting anything less hardy in that pot. Even if your recipe says so.
Also, btw- this is not a food blog.
**I’m going to break my own rule just for history and palate purposes- here’s an actual recipe from a book we used 12 years ago:

Put COOKED RICE in your slow cooker for 6-8 HOURS???!!!! With bell peppers and canned beans…. What is wrong with you?
Here’s the book that you don’t need to buy unless you need kindling:

Crockery indeed.