For garlic and thyme oil, heat ingredients in a small saucepan over medium heat until fragrant and garlic is light golden (2-3 minutes), then set aside.
Preheat a sandwich press. Drizzle cut sides of ciabatta with a little garlic and thyme oil and spread bases with 'nduja. Top with mozzarella slices, season with sea salt and sandwich with tops. Toast until mozzarella melts (3-4 minutes), then cut into pieces, drizzle with garlic and thyme oil, and serve hot with pickled onions.
