Increase the oven temperature to 400 degrees.
In a small saucepan combine ½ cup water and ½ cup sugar, sichuan peppercorns, lime juice and half the lime zest.
Stir until the sugar has dissolved and the syrup has thickened a bit, about 3 - 4 minutes. Remove the pan from the stove and let steep.
Line a sheet pan with parchment paper. Peel and core the pineapple and cut into 1 inch chunks.
Place the pineapple on the prepared sheet pan. Drizzle with the sechuan syrup, tossing to coat the pineapple.
Roast the pineapple for approximately 20 minutes, stirring halfway.
While the pineapple is roasting, make the rum lime syrup.
In the same saucepan you made the sichuan syrup, add ½ cup water, remaining granulated sugar, brown sugar, remaining lime zest and vanilla seeds.
Bring the mixture to a boil over medium heat to dissolve the sugar. Cook for approximately 5 minutes.
Remove from the heat and let cool. When cool, stir in the rum.
To Serve: Slice the cake into 8 pieces and top with some of the caramelized pineapple. Drizzle some of the lime and rum syrup over and garnish with toasted coconut.