Preheat oven to 350F.
Lightly grease a 9.5 inch baking dish with cooking spray and set aside.
In a large bowl, combine sliced sweet potatoes, flour, salt, pepper, ginger, nutmeg, pepper, and thyme; toss to combine.
Arrange one layer of sliced sweet potatoes, overlapping slightly, on the bottom of prepared baking dish.
Sprinkle with a bit of parmesan and pour about 1/4 cup of evaporated milk.
Repeat layers with remaining sweet potatoes, parmesan, and milk.
Top with swiss or gruyere cheese.
Cover with foil and bake for about 35 minutes.
Remove foil and continue to bake for 25 more minutes, or until top is browned and bubbly.
Remove from oven and let cool for 30 minutes.
Garnish with grated parmesan and dried parsley.