Slow Cooker Mushrooms and Rice

long grain rice

dairy free butter (melted)

onion (chopped)

portabello mushroom soup (it comes in a box, you can also use your favorite mushroom soup - if it is condensed make it at least 16 oz. of soup and the rest liquid - just add enough water or vegetable broth to make 32 ounces)

mushrooms (sliced)

sea salt (- it seems to need this much salt to balance the mushrooms - you can just add 1 teaspoon until after cooking and see if you want to add the other teaspoon)

black pepper