Slice each sweet potato into 1-1 1/2 inch coins, discarding the ends.
Add the potatoes to a large pot of salted water and bring it to a rolling boil. Reduce the heat slightly and boil the potatoes (covered) for 20-25 minutes, or until easily pierced by the tines of a regular dinner fork.
Transfer the potatoes to a colander to drain. Run the potatoes under cool water briefly to stop them from cooking more. This will keep them from getting so tender they fall apart in the next step.
Spray a large baking sheet with non stick cooking spray and transfer the sweet potato slices evenly out on to it.
Using a fork, lightly press down on each slice- just enough to crack them open slightly. Be careful not to apply too much pressure and actually mash them. You want them to hold their shape.
In a small mixing bowl, whisk together the butter, garlic, and parsley until evenly combined. Pour the seasoned butter evenly out over all the sweet potato slices. Use a silicone brush to lightly spread the butter mixture evenly over each slice.
Sprinkle the potatoes with salt & pepper, to taste.
Set the oven to broil on high heat, and cook the potatoes for 15 minutes- watching carefully so they don't burn, just until they're lightly browned and beginning to crisp.
Remove the potatoes from the oven, sprinkle them evenly with the Parmesan cheese, and return them to the oven just long enough for the cheese to melt.
Let the potatoes rest for about a minute before serving. Serve with extra seasoned butter for drizzling or dipping, if desired.