Bring a saucepan of water to the boil then add the linguine and cook according to the instructions on the packet, until al dente, about 9 to 10 minutes.
Meanwhile spray oil into a frying pan over a medium heat and fry diced up chicken with black pepper and Cajun spice and cook until chicken has a nice colour and is no longer pink in the centre, about 8 minutes.
Add the onions, peppers and chilli and cook for another 3 to 4 minutes. Drain linguine and add to the chicken mix.
Add chilli flakes and garlic butter and mix together to finish cooking. Spoon into warmed bowls and serve immediately.