This dessert sounds exotic but it is quite easy to make from softened sorbet and candied lemon slices.
Make the candied lemon slices: Prepare an ice-water bath. Bring a medium saucepan of water to a boil. Remove from heat, and add lemon slices. Let stand 1 minute. Using a slotted spoon, transfer lemon slices to ice-water bath. Let cool, then lay slices on parchment paper to dry.
Cut a round of parchment paper to fit inside a large shallow saucepan, and poke a hole in center; set aside. Bring sugar and 2 cups water to a boil in pan, stirring to dissolve sugar. Reduce heat to medium-low. Transfer lemon slices to syrup, and place parchment round directly on surface. Simmer until rinds are translucent, about 35 minutes. Remove from heat, and let lemon slices cool in syrup. Use immediately, or refrigerate in syrup in an airtight container up to 1 week.
Drain lemon slices. Line bottom third of a 5-quart bowl with slices. Freeze until set, 30 minutes. Line middle third of bowl with slices, and freeze 30 minutes. Line top third of bowl with slices, and freeze 30 minutes more. (Working in stages will prevent the lemon slices from falling to the bottom of bowl.)
Make the bombe: Spread lemon sorbet into bottom and up sides of bowl to make an even layer over lemon slices. Freeze until firm, about 1 hour. Fill bowl with coconut sorbet, and smooth top of bombe. Cover with plastic wrap, and freeze overnight (up to 2 days).
Dip bowl in hot water to make it easier to unmold. Invert onto a cake stand, and remove bowl. Serve, or freeze 2 hours more to firm the outside before serving.