To make the lime and chilli syrup, place all the ingredients in a small saucepan and stir over a low heat until the sugar has dissolved. Bring to the boil, then reduce the heat and simmer for 8–10 minutes until syrupy.
Meanwhile, heat a griddle pan. Using a sharp knife, remove the skins from the mangoes, then cut each one into thick slices either side of the stone. Place the mango slices on the hot griddle and cook for 4–5 minutes on each side.
Transfer to 4 serving plates and serve with the warm syrup drizzled over the top.