In a large, deep skillet, heat the vegetable oil. Add the onion and cook over moderately high heat, stirring, until golden brown. Add the lemongrass mixture and cook, stirring, until fragrant, about 2 minutes. Add the ground pork and cook, breaking up the meat, until no pink remains, about 3 minutes. Add the coconut milk and reduce the heat to moderate. Stir in the red curry paste, Sriracha and lime juice and turn off the heat.