Medi For All Tips:
Use olive oil instead of butter. This will also make the recipe vegan.
Use any kind of mushrooms you like.
You can substitute dried mushrooms in this recipe - rehydrate in hot water for 15 minutes before starting.
You can use frozen spinach in this recipe, but make sure you thaw and wring dry very well, to avoid making your oatmeal watery.
Use chicken broth if that's what you have, rather than buying vegetable broth. (This will mean the recipe is no longer vegetarian.)
Oats of all kinds can often be found in your grocery store's bulk section. Save money and only buy what you need for this recipe if oats aren't something you use often.