Marinade the pork fillet and prawns with the garlic, lime juice and the honey-mustard sauce. Grill the meat and prawns just before serving, brushing with the marinade from time to time to prevent it from getting dry. In a mixing bowl, whisk together the soy sauce, rice vinegar, sesame oil, sugar, spring onions, sesame seeds and vegetable oil. Cook the soba noodles according to packet instructions. Drain from the cooking water and stir in the soy sauce marinade. Serve the noodle salad at room temperature accompanied with slices of grilled pork and prawns.