Melt the butter in a very large (12-inch) skillet over medium-high heat. Add the onion and cook, stirring regularly, until richly caramelized, about 10 minutes.
In a large (10-inch) skillet over medium heat, cook the bacon, turning every once in a while, until browned and crispy, about 10 minutes. Drain on paper towels, then chop into small pieces.
Place turnips in a microwave-safe bowl, add 1 tablespoon of water and cover with plastic. Poke holes in plastic and microwave for 4 to 5 minutes at 100% until turnips are nearly tender.
Drain the turnips and add to the skillet the Sriracha and agave syrup. Cook until sauce is reduced and turnips are coated, about 2 minutes. Stir in blue cheese and parsley.
Scoop onto a serving plate and top with more parsley leaves.