Preheat oven to 350°F. Place graham crackers and coconut in the bowl of a food processor; pulse until finely ground. Add brown sugar, flour, and salt and pulse to combine. Add coconut oil and pulse until mixture holds together when pinched. Press into bottom and up the sides of a 9-inch fluted tart pan with a removable bottom. Bake until golden brown and set, 12 to 15 minutes (carefully tent edges with foil if browning too quickly.) Let cool completely on a wire rack.
Filling + Topping
Make filling: in a small bowl, sprinkle gelatin over 2 teaspoons cold water. Place granulated sugar, lime zest, lime juice, egg yolks, salt, and butter in a medium saucepan over medium heat, whisking until butter melts. Bring to a simmer and cook, whisking often, until mixture thickens enough to coat the back of a spoon, about 5 minutes. Remove from heat and whisk in gelatin. Strain mixture through a fine-mesh sieve into cooled tart shell. Refrigerate until set, at least 2 hours and up to 1 day, covered.
Make topping: in the bowl of a stand mixer, beat coconut cream with whisk attachment on medium-high speed until soft peaks form, 6 to 8 minutes. Transfer to a small bowl; cover and chill until thickened slightly, at least 1 hour. Just before serving, spread mixture over top of tart; sprinkle with toasted coconut flakes and lime zest.