Chopped up over ripe tomatoes, a couple of onions chopped & fried (or they taste a bit raw), chicken thighs cut up, rolled in flour & seared in the onion pan.
Add any other vegetables eg. carrots, peppers, courgettes, aubergine but be aware they cook down really soft - my kids prefer veg cooked separately on the side.
Add garlic (lots) & an optional chilli - again they cook down loads so chop both coarsely, no need to mince finely.
Add flavourings/liquid. Be really mean with the liquid or you'll end up with soup! Lots cooks out of tomatoes & chicken so you need much less than you'd think.
I use: half tin coconut milk with curry spices OR tomato puree, dollop of stock, herbs usually. However, most popular effort recently was when I had a nearly empty bottle of barbecue sauce & rinsed it out into the pot!
Also experiment with chilli & liquid smoke OR soy sauce OR various vinegars...
Cook for 4 hours on high or all day on low. Add frozen veg or tinned pulses as liked for last hour.
You can do the same thing with stewing steak - stew, curry, chilli.
I also do a mean stealth veg tomato sauce - 2kg over ripe tomatoes, rest of the veg in the fridge, garlic, herbs, cup of stock. Leave to tick away all day in low then blend. Freezes brilliantly.
I'm in a hot country where veg are dirt cheap, great quality but don't keep, so forever using slow cooker to batch cook for freezer. Best £25 I ever spent.