Cut the papaya in half lengthwise, scoop out and discard the seeds, peel the skin, and cut the flesh into rough 1-inch (2.5cm) chunks until you have 2 cups (300g). For a colder, thicker smoothie, spread the chunks on a parchment-lined baking sheet and freeze for 1 to 2 hours before blending.
Peel the banana, slice into 1/2-inch (1.25cm) rounds, and freeze in a zip-lock bag or on a lined tray for at least 2 hours or overnight. A frozen banana is essential for achieving a thick, creamy, milkshake-like texture.
Cut the lime in half crosswise and use a citrus juicer or reamer to squeeze out 1 tablespoon of fresh juice, catching any seeds before they fall in.
Pour the 1 cup (240ml) of coconut milk into the blender first, then add the papaya chunks, frozen banana slices, lime juice, honey, vanilla extract (if using), and ice cubes (if using fresh fruit).
Secure the blender lid and blend on high speed for 45 to 60 seconds until completely smooth; stop halfway to scrape down the sides if needed, and add a splash more coconut milk if the blender is struggling.
Taste the smoothie before pouring; if you'd like it sweeter, add a little more honey and blend for another 5 to 10 seconds.
Divide the smoothie evenly between two tall glasses, garnish with a papaya slice on the rim and a lime wedge if desired, and serve immediately for the best texture and flavor.