Mix together the brown sugar, 1 teaspoon black pepper, thyme, cumin, 1 teaspoon of garlic salt, paprika, chilli powder and nutmeg in a bowl until thoroughly combined. Rub both sides of chicken breasts with the spice mixture then place into a 22x22cm baking dish. Sprinkle any remaining seasoning mix on top of chicken if desired.
Bake in the preheated oven until the chicken is lightly browned, no longer pink inside and the juices run clear, about 30 minutes.
While chicken is baking, bring the rice and water to a boil in a saucepan over high heat. Reduce heat to medium-low, cover then simmer until the rice is tender and the liquid has been absorbed, 20 to 25 minutes.
Chop half the pineapple slices. Mix the chopped pineapple, coriander and olive oil into the cooked rice then season to taste with a pinch or two of garlic salt and black pepper. Fluff the rice up with a fork then transfer to a serving plate. Serve with the baked chicken, topped with remaining pineapple slices.