Preheat oven to 350˚F. Arrange potato slices in a single layer on one or two large baking sheets. Stir together onion, oil, lemon, garlic, and pepper, and brush mixture over both sides of potatoes.
Bake for 20 minutes or until potatoes are tender. Turn oven to broil, and broil 3 to 5 minutes or until browned. Sprinkle with parsley before serving, if desired.