Put a large saucepan of water on to boil then add spaghetti and cook for 12 minutes.
Meanwhile, fry the bacon in a frying pan for 5 minutes. Add the chicken and red capsicum then cook for about 5 minutes or until chicken is cooked.
Drain the spaghetti and add to the frying pan with the chicken mixture; stir it all together. Place in an ovenproof dish.
To make the cheese sauce melt the butter in a saucepan then add the flour to make a roux and cook for 2 minutes. Add the milk and stock then bring to the boil stirring continuously until thickened. Once thickened add the cheese and stir in until it has melted.
Pour cheese sauce over the spaghetti mixture and bake for 25 minutes.