Hi molly the problem is if you don't fry the onions first, due to the low cooking temperatures, they won't soften.
Back in the UK when I was working and bringing up my 2 boys on my own I used the slow cooker a lot so that there was a meal ready when I got in from work.
I used to batch fry a big load of onions then freeze them in small bags for use in slow cooker recipes.
I rarely pre-fried the meat even if the recipe said so. It makes little difference to taste just the appearance but if you make the sauce thick enough it doesn't show.
Rabbit stew cooked with prunes is good in the slow cooker as a winter dish. I don't have the recipe though, sorry. I just used to make it up as I went along.
Brian.