Prepare the sauce by combining the sugar, chilli flakes, ginger, peanut butter and tomato paste in a bowl.
Slowly stir-in the water a little at a time until the sauce is smooth.
Add the oil to a large pan and fry the chopped onion until translucent. Add the chicken and continue frying until the chicken has begun to brown before adding the bell pepper. (Can add a chopped and seeded hot pepper if you like a little more heat!).
Continue cooking until the chicken is nicely browned all over.
Pour-in the peanut sauce and diced tomatoes and stir well.
Cover and reduce the heat to low simmer.
Cook for 45 minutes to 1 hour, stirring occasionally. Taste and add salt if needed.