Turn the oven on to its lowest setting. Measure the oil into a very large (12-inch) skillet and set over medium-high heat. If the skin of the 2 halves of the trout is still connected, cut them apart, making 2 fillets. Sprinkle the fish generously with salt and lay skin side up in the hot oil. Cook until golden underneath, 2 to 3 minutes. (If they don't fit comfortably in the pan, cook them in 2 batches.) Use a spatula to turn the fish and cook for a minute longer, until the flesh separates from the skin (use a corner of your spatula check at 1 edge). With the spatula, transfer a pair of fillets to each of 4 dinner plates, flipping them skin side down. Keep warm in the oven.
Reduce the heat under the skillet to medium. Add the garlic and cook a few seconds until fragrant, stirring constantly. Pour the broth into the skillet, and add 1/2 teaspoon salt and the green beans. Cover the skillet (a cookie sheet works, if you don't have a lid large enough) and cook until the green beans are barely tender, 6 to 7 minutes.
While the green beans are cooking, cut the chile(s) in half lengthwise and scrape out the seeds. Chop finely.
When the beans are ready, uncover the skillet and add the chile(s). Increase the heat to high and cook for a minute or so to concentrate the broth. Then add the macadamias, cilantro, and lime juice and mix well. Taste and season with salt, probably another 1/2 teaspoon. Spoon a portion over each fillet and dinner's ready. Serve with Roasted Poblano Mashed Potatoes, if desired.
In a large saucepan over high heat, add potatoes, salt, and enough water to cover. Bring to a boil, reduce to a simmer, and cook, uncovered until soft, about 20 minutes. At the same time, in another small saucepan over low heat, add milk, butter, and chiles and heat until butter is melted. Keep warm.
Once the potatoes are tender, drain them and mash with a potato masher. Pour the milk mixture into the potatoes and stir to combine. Season, to taste, with salt and pepper. Serve hot.
Recipe courtesy Rick Bayless, adapted from Mexican Everyday, published by W. W. Norton & Co., 2005