Preheat the oven to 180°C.
Slice the sweet potatoes into 2mm slices. You could use a mandoline to make this easier, or just use a sharp knife.
Arrange the slices of sweet potato in rows along the length of the dish, overlapping each slice.
In a small bowl combine the paprika, garlic granules, onion powder, salt and pepper. Spray the potatoes with low-calorie cooking spray and sprinkle over the spice mix.
Dot the thyme stalks around the slices of potato and pop the dish into the oven for 40 minutes.
After 40 minutes remove the dish from the oven and sprinkle over the Parmesan cheese. Place back into the oven for a further 20 minutes. The potatoes should be cooked through and the Parmesan cheese golden brown. Serve!