Bake the empty pie shell according to the package directions; cool completely. Arrange the banana slices in the pie shell. Combine the sugar, cinnamon, salt, lime juice, and 1 1/2 cups of the guava nectar in a small saucepan and bring to a bare simmer over medium heat.
Put the cornstarch in a small bowl. Add the remaining 1/4 cup guava nectar to the cornstarch and whisk to combine. Pour the cornstarch mixture into the saucepan and whisk to combine. Bring to a boil and cook, whisking constantly, until thickened, about 2 minutes.
Turn off the heat and whisk in the butter. Pour the guava pudding into the pie shell. Cool to room temperature, then refrigerate until set, about 2 hours.
Serve with coconut ice cream.