For the pineapple: Preheat the oven to 425 degrees F.
Begin by peeling the pineapple and cutting it into 1/2-inch-thick planks approximately 2 by 2 inches wide; discard the core. Arrange in a single layer in a roasting pan. Whisk together 1/2 cup water, the rum, sugar, vanilla and salt, and then pour over the pineapple. Sprinkle the top with a little extra sugar, if desired, then roast until caramelized, 17 to 18 minutes. When done, remove the pineapple from the pan and allow to cool slightly before dicing.
For the pecans: Arrange the pecans in a baking sheet and toast until slightly darkened and fragrant, 7 to 8 minutes. Remove from the oven and allow to cool slightly before adding the butter to the baking sheet. Immediately toss the baking sheet to coat the pecans as the butter melts. Sprinkle evenly with the sugar and salt and toss once more. Set aside on a plate to cool.
To assemble, place 2 to 3 scoops of vanilla bean ice cream in a bowl. Top with 2 to 3 spoonfuls of rum-roasted pineapple and garnish with sugared pecans.