MIX olive oil, garlic, salt, pepper and onion powder; set aside.
CUT very thin slice off bottoms of potatoes (to make stable); discard. Pierce each potato several times; microwave on HIGH 10 minutes or until almost tender.
HEAT oven to 450ºF.
MEANWHILE, make 12 crosswise slices on tops of each potato, stopping about 1/2-inch from bottoms. Carefully separate slices slightly. Brush potatoes with olive oil mixture (inside and out); top with Cheddar cheese, pressing into slices. Place in baking pan.
BAKE 15 to 18 minutes, or until thoroughly heated and cheese is melted. Remove from oven; sprinkle with Parmesan cheese. Broil 2 to 3 minutes or until light golden brown. Sprinkle with chives.