Yum! I just made these for lunch, and they are so easy to make, and soooooo good.

Filling:
1 tbsp butter
1 small can sliced mushrooms
1 cup mashed potatoes
1/4 cup cheddar cheese, grated or shredded
1/4 cup parmesan cheese
salt and pepper to taste

Dumplings:
16 wonton wrappers (you can get these at walmart or any other grocery store in the produce section, I think)
2 tbsp water
1 tbsp vegetable oil

Boil potatoes for mashed potatoes.   Saute mushrooms with butter and add salt and pepper.   In a small bowl, combine mashed potatoes and mushrooms.  Mix well and add cheeses.   Season with salt and pepper.

Lay out wonton wrappers, place a small spoonful of the mixture onto them, and with a pastry brush (or your finger), brush water around the edges of the wrapper, then fold in half and seal it.  
Fry wontons in a skillet for about 2-3 minutes, flipping once, on medium high heat.
Lay fried wontons on a washcloth or napkin to allow to dry.    Let cool, then enjoy!