Heat the oil in a large pan over a medium heat, then add the onions and cook, stirring occasionally, for 6 minutes. Add the garlic and ginger and cook for another 2 minutes, until the onions are soft and golden brown.
Add the garam masala, ground coriander, ground turmeric, chopped green chillies and chicken breasts, and cook, stirring, for 3 minutes to seal the chicken and coat it in the spices.
Add the chopped mango, salt and 400ml/14fl oz of boiling water to the pan and stir to combine. Bring to the boil, then reduce the heat to a simmer, cover with a lid and leave to cook for 12 minutes, until the chicken is cooked through and the sauce has thickened and reduced.
Remove from the heat and stir through the sugar, almonds, crème fraîche and coriander/cilantro. Serve hot, with your choice of rice or flatbreads alongside.