If toasting macadamia nuts, preheat your oven to 350 degrees C. Pop them in there until just lightly browned, around 6 or 7 minutes.
Preheat your grill to high.
While the grill is preheating, dice the sweet onions and ginger.
Add the oil to a medium sized pan and preheat over medium heat.
Add the sweet onions and ginger and cook until soft (about 5 min)
Throw your fish on the grill. it will take around 5-7 minutes per side, depending on how thick your fillet is. Only flip it once.
While your fish is grillin' away, add the pineapple juice, orange juice or syrup, coconut milk, soy sauce, rice vinegar, fish sauce, sweetener and pinch of salt to the pan. Stir until it just all combines.
Mix the cornstarch with 1 tbsp. water and 1 tbsp. of the sauce from the pan and add it into the mix.
Stir, and bring to a boil.
Turn down the heat to medium low and let it simmer until nice and thick (about 5 min.)
Transfer your fish to plates and spoon the sauce over. Garnish with the macadamia nuts, and green onion and cilantro if your heart desires. I used all the garnishes and it was amazing. I also served it over cous cous which absorbed all the saucey goodness and tasted amazing!