Place a large heavy-based saucepan over high heat and add the sesame oil. Cook the chicken in two batches, turning regularly for about 5 minutes or until browned. Remove from the pan and set aside while you cook the remaining chicken. Remove it from the pan.
Reduce the heat a little and add the butter. When the butter has melted add the spices and cook, stirring, for 4-5 minutes until fragrant. Return the chicken to the pan, along with the tomatoes
and tomato paste. Stir and simmer for about 20 minutes. Turn down the heat to low and stir in the coconut milk. Simmer for about 5 minutes.
Mix the banana and coconut together in a small bowl. Serve the butter chicken with the brown rice, chilled cucumber, banana with coconut and some mango chutney, if desired.