Poke the sweet potatoes along their sides with a fork. Microwave the sweet potatoes, laid out in a circle in the microwave, until soft, 10 to 15 minutes.
Slice the potatoes, across their width, into 1/2-inch slices. Separate them so they're not sticking together. Put 1/4 cup of olive oil into a small cup. Brush that oil onto the flat surfaces with a pastry brush. Pour any remaining oil over potatoes.
Put the oiled sweet potatoes into a gallon-sized zip-top bag. Add Parmesan cheese, garlic powder, and salt. Shake the bag thoroughly for 1 minute. Manipulate the pieces with your hand (from the outside) to make sure all pieces get exposed to the cheese and powder.
Heat remaining 1/2 cup of olive oil in a skillet over medium-high heat. Carefully pour the sweet potatoes into the skillet. Cook, moving the pieces around and flipping periodically, for 7 minutes. Remove from heat and serve.