Peel and coarsely chop the garlic. Sprinkle it with a generous pinch of salt and mash it to a paste with the side of a chef’s knife. Transfer to a small bowl and stir in the oil, lemon zest, coriander, and 1 Tbs. salt.
Put the pork on a large rimmed baking sheet, pat dry with paper towels, and rub all over with the salt mixture. Let sit at room temperature for at least 1 hour and up to 2 hours.
Position a rack in the center of the oven and heat the oven to 350°F. Roast the pork until an instant-read thermometer inserted in the thickest part reads 130°F, about 50 minutes.
Meanwhile, peel and core the pineapple. Cut half into small dice and roughly chop the other half. Purée the roughly chopped pineapple in a blender, then strain it through a fine strainer, pressing on the solids with a spoon, to yield about 3/4 cup juice. In a small saucepan, combine the strained pineapple juice and maple syrup and cook over medium-high heat until reduced to 1/3 cup, 12 to 15 minutes. The liquid will become very bubbly as it reduces; lower the heat as necessary.
Set aside all but 2 Tbs. of the reduced liquid (this will be your glaze). Add the vinegar, shallot, cayenne, and a pinch of salt to the 2 Tbs. liquid remaining in the saucepan and cook over medium heat just until the shallot begins to soften, about 2 minutes. Add the diced pineapple and scallion whites and continue to cook, stirring frequently, until the pineapple softens and releases some of its juice, 3 to 5 minutes. Remove from the heat and let cool slightly.
When the pork reaches 130°F, brush it with some of the glaze and continue to roast, brushing with more glaze every 5 minutes, until an instant-read thermometer inserted in the center of the roast reads 145°F, about 20 minutes more. Let rest for at least 10 minutes before serving.
When ready to serve, stir the scallion greens and cilantro into the chutney. Slice the pork into 1/2-inch-thick rounds and serve with the chutney.
