Bring 5 cups of water to a boil in a medium pot. Add the sago and cook uncovered for about 10 minutes, stirring occasionally, until the pearls turn mostly translucent. Turn off the heat, cover with a lid, and let sit for 5 minutes. Drain and rinse the sago under cold water for about 15 seconds to stop the cooking. Transfer to a bowl, mix with ¾ cup coconut milk, and refrigerate until chilled.

While the sago cools, add the diced avocado (reserving a few cubes for garnish), remaining coconut milk, sweetened condensed milk, and optional pandan extract to a blender. Blend until completely smooth. Transfer to a bowl and refrigerate for at least 1 hour.

In 2-3 small glasses, pour alternating layers of the avocado mixture, then coconut sago mixture, then another layer of the avocado mixture. Garnish with reserved avocado cubes, a mint leaf, and a drizzle of sweetened condensed milk before serving.