River Steam Boat

1 tablespoon vegetable oil 2 cloves garlic, finely sliced 2 red Asian shallots, finely sliced One 1-inch piece fresh ginger, peeled and finely sliced 1 small onion, cut into wedges 1 tablespoon tamarind pulp with the seeds (not tamarind puree) 2 teaspoons chili flakes 4 cups young coconut juice 1 tablespoon fish sauce 1 tablespoon unsalted roasted peanuts 1 tablespoon soy sauce 1 tablespoon caster (superfine) sugar 2 eggs, beaten 1 bruised lemongrass stem Juice of 1 lime Sea salt 1 pound 2 ounces whole white-fleshed fish, such as snapper, cut into fillets and finely sliced, bones reserved 1/2 teaspoon freshly ground black pepper 16 butter lettuce leaves 7 Chinese cabbage leaves, finely sliced 4 spring onions, cut into 1 1/4-inch pieces 1 large handful fresh cilantro, roughly chopped 1 large handful fresh mint leaves 1 large handful water spinach, torn into 1 1/4-inch pieces