Make the granita: Heat the water, sugar, and salt in a small saucepan over medium heat, stirring until the solids are fully dissolved. Remove the pan from the heat, add the tequila, and allow the mixture to cool fully. Add the lime zest and juice, stir to combine, and pour the mixture into a small metal (accelerates the rate of freezing) baking pan, 8 by 8 inches. Freeze for 45 minutes or until beginning to freeze, then use a fork to rake the frozen areas fluffy. Return the granita to freezer for another 30 minutes. Bring out to rake again, paying special attention to the edges of the pan. Repeat raking and breaking the mixture up until fluffy, every 30 minutes until fully frozen (21⁄2 to 3 hours). Granita can be made up to 3 days in advance, covered, and kept frozen. Scrape the surface to refluff it when serving. Make the cashew brittle: Over medium heat, transfer the sugar to a small sauté pan and warm until it begins to melt. Once the sugar is nearly melted, about 5 minutes, add the cashews. When the sugar has fully melted, quickly stir to thoroughly coat the cashews using a silicone spatula, turning the heat down as needed so the cashews do not burn. The sugar will turn deep golden and caramelize: scrape the mixture out of the pan onto a parchment-lined tray. It will immediately solidify, so work swiftly to get it all out and in one piece. Set aside to harden while you sear the pineapple. This step can be done 1 day in advance and kept on its tray in the refrigerator. Trim the skin and fibrous core of the pineapple and slice it crossways into 1⁄2 by 2-inch segments. In a small nonstick pan set over medium-high heat, drizzle the oil once the pan is hot. Swirl the pan to coat, then arrange the pineapple and sear undisturbed for 2 minutes. Turn once the first side is burnished in parts, then sear for another 1 to 2 minutes. Turn the pieces onto their ends and sear for another minute, then transfer to a plate to cool. Combine the Aleppo chile flakes and flake salt in a small bowl and stir together until uniform. Divide the pineapple evenly among the plates. Break the cashew brittle into shards. Spoon the granita into the center and arrange the brittle toward the edge of each plate. Sprinkle the chile salt across the pineapple and granita and serve.