Prep the guava: Wash and slice the guavas.
Scoop out the seeds if you prefer a smoother texture, then chop the flesh. If using very seedy guava, you can blend and strain later.
Build the base: Add guava, yogurt, milk, banana (if using), and a pinch of salt to the blender.
Sweeten and brighten: Add honey or agave to taste and a squeeze of lime juice if you like a tangy edge.
Ice and blend: Add the ice and blend on high until smooth and creamy. If it looks too thick, splash in a little more milk.
Adjust and refine: Taste and tweak the sweetness.
For a silky texture with seedy guavas, strain through a fine-mesh sieve, then return to the blender for a quick pulse.
Serve immediately: Pour into a chilled glass and garnish with mint or a slice of guava if you’re feeling fancy.