1) Preheat the oven to 200C/Gas 6.
2) Season the chicken all over with salt and black pepper and place in a greased shallow roasting pan. Brush the mustard all over the top of each chicken breast, then spread with the goat's cheese.
3) Place the macadamia nuts in a plastic bag and smash with the flat side of a meat mallet or bottom of a heavy skillet until finely crushed. Sprinkle the nuts over the goat's cheese. Cover the pan with foil and bake for 20 minutes. Uncover and bake for 5 to 10 more minutes, until the cheese is golden brown and the chicken is cooked through.
4) While the chicken is baking, cook the couscous according to the package directions. Fluff with a fork and stir in the pimentos, parsley and salt and freshly ground black pepper, to taste.
Serve half of the chicken and all of the couscous. Reserve the remaining chicken for a chopped salad, if desired.