Heat oil in a wok over high heat. Add eschalot, garlic, lemongrass, lime leaves, ginger, galangal, coriander stems and chilli, and cook for 5-6 minutes or until caramelised and fragrant. Add fish sauce, sambal oelek and tomatoes, and cook for 6-8 minutes until softened and juicy. Add the pipis, cover with a lid and cook for 6-7 minutes until the pipis have opened. Discard any unopened pipis. Serve topped with extra chilli, coriander leaves and lime wedges.