These are my options on SQ321 (J):
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LHR-SIN (SUPPER)
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Biryani Chicken
Fragrant basmati rice cooked with aromatic herbs and spices, topped with chicken and served with raita
Braised Beef Short Ribs
Braised short ribs of beef served with potato puree, red chard and horse radish cream
Chicken Rice
Poached chicken, sliced and served on long-grain rice cooked in chicken broth. Accompanied by dark soya sauce and fresh chilli sauce.
Chicken with Pecan
Nut crusted roast chicken breast with pecan, almond and maple syrup crust, served with sweet potato mash and vegetables with chorizo
Grilled Beef Fillet
Served with selected fresh market vegetables and potatoes
Grilled Monkfish
Grilled monkfish served with mushroom sauce, crushed potatoes and vegetables
Grilled Salmon Fillet
Served with asparagus, fried capers and vinaigrette
Prawn Wanton Soup
Oriental noodle soup served with prawn wantons, shiitake mushrooms and bok choy
Roast Duck with Rice
Cantonese roast duck served with vegetables and steamed rice
Sesame Fried Seabass
Deep fried seabass with sesame seeds, egg fried rice, vinegar sauce and stir fried vegetables
Thai Beef Curry
Beef simmered in Thai red curry and served with stir-fried vegetables and steamed jasmine rice
Vegetable Kebab
Vegetable kebabs served with cous cous and mint yoghurt dressing
My much less informed opinion is, after the lobster thermidor, there is no real signature or novel or very, very well done dish for BTC. They should all be OK and part of it is the novelty of having a fine dining meal in the middle of a flight and not the quality of the fine dining meal in absolute terms (which obviously will fall short of normal fine dining).
Order what you like and enjoy it with that mindset. Even the hawker meals converted to Business Class BTC meals might be enjoyable, as Milelion argues.