Halve the pineapple lengthwise, leaving the leafy top intact and cutting through it. Hollow out each half (a serrated, curved grapefruit knife works well). Chop 1 cup of the fruit very small and set aside for the rice. Cut the remaining pineapple into ½-inch cubes and set aside for garnish.

Crumble the cold rice between your fingers to separate the grains and set aside. Heat 1 tablespoon of the oil in a large nonstick skillet or wok over high heat, swirling to spread it in the bottom of the pan.

Add the onion and mushrooms and stir-fry until they start to soften. Add the garlic and red pepper flakes and stir-fry for about 1 or 2 minutes. Add the ginger and stir-fry for another minute. Add the remaining tablespoon of oil and the cold rice to the pan. Stir-fry for 2 or 3 minutes over high heat, then add the green beans, tofu, and the 1 cup of chopped pineapple and stir-fry for 2 or 3 minutes more. Add the cashews, soy sauce, and sugar and stir-fry until the ingredients are well combined and rice is heated thoroughly, about 5 minutes. Turn the heat down a little if it seems to be sticking and browning. Add black pepper to taste.

Remove the pan from the heat and fill each half of the prepared pineapple evenly with the hot rice. Garnish with extra chunks of the pineapple, the sliced green onions, and coconut, if using. Serve immediately.