Use the discarded mushroom stems for another dish, or save them to make vegetable stock. You could even dice them and cook them with the brown rice mixture for an extra mushroomy bite. Don’t have thyme? Sage or italian seasoning would go nicely in these risotto stuffed mushrooms.
You could leave out the cheese and simply mix the seasonings and aromatics with the rice to stuff in the mushrooms.
A little bit of cooked sausage crumbles could be a nice addition to the rice mixture. Any leftover chicken, pork chop, or ground turkey would be good too.
This “risotto” is perfect for leftover grains and any bits of vegetables. Quinoa or barley would be a nice swap for the brown rice. You could even use leftover farro. If you’re looking for a softer texture on a grain like farro, you can simmer the cooked grains in a bit of extra white wine or broth to help them plump up.