Place half of the mango slices into the bowl of a blender with the coconut milk. Blend until smooth.
Heat the oil in a large saucepan over medium-high heat. Cook the curry paste, stirring, for 2 minutes or until fragrant. Add the chicken and shallots and cook for 5-7 minutes or until the chicken is just cooked through.
Pour in the mango puree and cook until heated through. To serve, stir in the remaining mango slices and cucumber.