Preheat oven to 350°F. In a medium bowl, combine graham cracker crumbs, kosher salt, brown sugar, and toasted coconut. Stir in melted butter until mixture resembles wet sand and holds together when squeezed.
Press crust mixture firmly into the bottom and up the sides of a 9-inch tart pan. Use the bottom of a measuring cup to pack evenly. Bake for 10 minutes, then cool completely on a wire rack.
Reduce oven to 325°F. In a heatproof bowl, whisk together mango puree, lime zest, lime juice, vanilla, sugar, salt, and egg yolks until completely smooth.
Set bowl over a saucepan of simmering water (double boiler), ensuring bottom doesn't touch water. Stir constantly for 20 minutes until curd thickens and coats the back of a spoon.
Remove from heat and immediately whisk in 4 tablespoons butter pieces until melted and glossy. Pour curd into cooled crust and smooth the top.
Bake for 15-17 minutes until edges are set but center still has a slight wobble. Cool to room temperature, then chill for at least 4 hours or overnight.
Before serving, top with Swiss meringue (if using) and torch until golden. Garnish with toasted coconut flakes, mango slices or flowers, lime wedges, and fresh mint.