Put the peppercorns in a dry frying pan and toast over a medium heat for 3 mins, stirring frequently. Tip onto a plate.
Put 2 tbsp oil in the frying pan, add the cauliflower and cook over a high heat for 5 mins to colour. Meanwhile, blitz the peppercorns in a small food processor or grind using a pestle and mortar and mix with the cornflour.
Drizzle the remaining 1 tbsp oil in the pan and add a third of the cornflour mix to coat the cauliflower. Cook for 1 min, then add the garlic, ginger, chilli, three-quarters of the spring onions and 400ml water.
Cover with a lid or baking tray and boil for a couple of mins. As this cooks, add the maple syrup, soy sauce and vinegar, plus 6 tbsp water, to the remaining cornflour mix in a separate bowl. Stir until smooth and set aside.
Add the maple cornflour mix to the cauliflower, stirring. Bring to the boil, then turn down the heat, add the beans, cover and simmer until the sauce thickens and the cauliflower is tender.
Tip onto a plate, scatter over the coriander, if using, then top with the remaining spring onions and the peanuts.