Steam pork belly in a steamer placed over a saucepan of boiling water until cooked through (15-20 minutes), then combine in a bowl with kecap manis. Preheat oil in a wok or deep-sided frying pan to 180C.
Meanwhile, for chilli palm sugar dressing, pound garlic and chilli in a mortar and pestle to a fine paste. Add palm sugar and lime juice, stir until melted, then add fish sauce.
Deep-fry pork in batches until golden (5 minutes, be careful as pork fat may burst while frying and oil may spit). Drain on absorbent paper, transfer to a bowl. Combine mango and herbs in a separate bowl, drizzle half the and to dressing over, add pork belly to combine. Serve fried immediately with shallots scattered over and remaining dressing and steamed jasmine rice to the side