I've been a load of wild mushrooms and a recipe for mushroom soup, that uses a slow cooker. I don't have a slow cooker. Would it work as well to use a cast iron casserole dish on a low oven for a couple of hours?
I see no reason why it wouldn't work in a low oven. I'd also say "no" to the microwave. I'm not a fan of them...and certainly not for cooking from scratch. You can't get the same depth of flavour.
Although I've got a slow cooker I often use my oven instead. (For example I cooked a chicken breast in mushroom sauce in a casserole dish for 3 hours at Gas Mark 2 earlier today). There's never any difference in the results.