You've been missing out on guanabana-flavored sorbet.
Bring the sugar and water to a boil until the sugar is dissolved, then reduce heat and simmer for about five minutes. Cool the sugar syrup, (leave aside about 6 tablespoons for later) and whisk it with the guanabána puree. Transfer to ice-cream maker. Remove mixture and let it harden in the freezer for a few hours. Blend the mango puree with the remaining syrup and about 6 tablespoons of water. Strain through a sieve, and whisk in the lime zest to make a coulis. Serve the sorbet with the coulis.