Preheat oven to 350ºF and lightly coat a 2-3 quart casserole dish with an oil mister.
Heat the oil in a large skillet over medium heat. Add the onion and cook until softened, about 6 minutes. Add the mushrooms and cook 5-6 minutes more, or until soft. Add the soup, kale and bulgur, then fill the can with water and add that to the skillet too; reduce heat to low and cover. Simmer for about 5 minutes, until mixture has thickened and kale has wilted.
Pour the veggie and soup mixture into the casserole dish. Top with the mashed potatoes (warming them first makes them easier to spread). Bake for 30 minutes, then turn on the broiler and broil for about 5 minutes before serving, or until potatoes are golden brown and slightly crispy in places.
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