Preheat oven to 350F.
Scrub potatoes, prick with a fork and microwave for five minutes. Carefully turn over, and microwave another 5 minutes. Once potato is soft, remove from microwave and allow to cool a bit. Half lengthwise and scoop flesh out into a bowl.
In a blender combine buttermilk, spinach and lime juice. Blend until smooth.
Beat buttermilk into bowl with potato until you get a fluffy mashed potato consistency. Stir in shredded cheese and season mixture with salt, pepper, and red pepper flakes to taste.
Divide green mash mixture among four potato halves. Top with additional shredded cheese.
Transfer potatoes to oven and bake an additional 10 minutes, or until cheese has melted and is golden on the edges.