Cook the diced chicken and the bacon. Cook the pasta and toss with olive oil.
Dice the onions and peppers and crush the garlic for the sauce, put in a saucepan with a little olive oil and sweat until soft. Add the rest of the sauce ingredients and base sauce. Cook for 15 minutes on a low heat. Taste and adjust seasoning if necessary.
To make the cheese sauce, melt the margarine in a saucepan then add the flour, and cook, stirring, until sandy in texture and colour. Add the milk in one go and whisk vigorously so that no lumps develop. Cook for about 5 minutes. Add the mustard and nearly all the cheese, reserving a little for the top, and allow to melt. If too thick, add a little more milk.
Add the cooked chicken, bacon and pasta to the tomato sauce and stir thoroughly.
Place into serving dishes, pour a little Cheese sauce over the top, sprinkle with grated cheese. Heat in the oven until the cheese is golden brown and the food is piping hot.