Wipe mushroom tops off with a wet towel and pick out the stems. In a medium skillet on medium-high heat, cook turkey meat through. Add chopped onions and seasonings. Cook until just about done, remove from heat and drain. Add 2 cups of cheese and mix together. Spoon mixture into mushrooms and place them on a baking pan or cookie sheet. Top with reserved cup of cheese. Place in 350 F oven for about 15 to 20 minutes, or until cheese is melted and mushrooms are soft.