Combine sliced yellow onions, olive oil, orange juice, lime juice, fresh cilantro, smashed garlic, salt, cumin, and cayenne in a bowl.

Place mahi mahi fillets in a large, non-reactive baking dish.

Pour the marinade over the fish, cover, and refrigerate for up to 1 hour.

Preheat a grill and lightly oil the grill rack with vegetable oil.

Remove the fish from the marinade.

Place mahi mahi skin side up on the oiled grill and cook until marked, about 45 seconds to 1 minute.

Turn carefully with a spatula and cook skin side down until the fish is just cooked through, about 4 minutes, depending on thickness.

Remove from the grill.

In a saucepan, combine coconut milk, water, salt, and sugar.

Bring to a boil.

Add long grain white rice, stir well, and reduce the heat to medium-low.

Cover and simmer undisturbed until the liquid is absorbed and the rice is fluffy, about 20 to 24 minutes.

Remove from the heat and let sit without stirring for 10 minutes.

Fluff with a fork and add chopped fresh cilantro.

Adjust seasoning to taste and serve hot.

Combine diced mango, diced avocado, diced fresh pineapple, minced red onions, minced red bell peppers, chopped fresh cilantro, fresh lime juice, minced jalapeno, minced garlic, and pinch of salt in a bowl.

Gently fold to combine the tropical salsa.

Adjust seasoning of the salsa to taste.

Let the salsa sit for 30 minutes before serving for the flavors to blend.

Spoon the coconut rice into the center of 4 large plates.

Arrange 1 mahi mahi fillet onto each serving of rice and top with the Tropical Salsa.

Garnish with toasted coconut and chopped cilantro, and serve immediately.