Melt the coconut oil in a frying pan over a medium heat. Add the onion and garlic and cook and stir until soft. Toss in the prawns and cook for around 2 minutes. Add the garam masala and stir well.
Cook for a further minute until aromatic then pour in the coconut milk along with the mango chutney and tomato puree. Stir well and cook on high until the sauce has thickened and reached the desired consistency and the prawns are plump and evenly pink. Stir through the mango chunks just prior to serving. Serve alongside some rice and naan bread.