Preheat the oven to 180 degrees C. Meanwhile, boil the pasta until al dente. Drain.
Melt the butter over medium heat in a saucepan. Add capsicum and cook 5 minutes. Sprinkle over the flour and stir well. Gradually pour in milk, whisking as you go. Add salt, pepper and nutmeg then cook, whisking, until thickened, about 5 minutes. Stir in smoked chicken and gruyere.
Stir in the pasta then transfer to a baking dish. Sprinkle with the Parmesan and bake 25 minutes or until golden.