GRILL DIRECTIONS: Scrub potatoes; prick skin several times with fork. Place on paper towels in microwave oven. Microwave on HIGH for 10 to 15 minutes or just until tender, turning potatoes over once halfway through cooking. Let stand 10 minutes.
Heat grill. Cut potatoes in half lengthwise. Scoop out 1 tablespoon pulp from each half and discard. Sprinkle potatoes with salt. Layer 3 spinach leaves in hollow of each potato half. Top each with mushrooms and 1 tablespoon sour cream. Sprinkle each with cheese and chives.
When ready to grill, place potatoes on gas grill over low heat or on charcoal grill near medium-low coals; cover grill. Cook 10 to 15 minutes or until potatoes are thoroughly heated and cheese is softened.