Prepare the toasted coconut: Spread coconut shavings evenly on a baking sheet and toast in a preheated toaster or skillet over medium heat. Stir frequently until golden brown and fragrant, about 2-3 minutes. Remove from heat and set aside.
Measure and prep fruits: Place frozen mango and pineapple chunks in the blender. Add coconut milk, sugar (if using), and ice cubes.
Blend ingredients: Secure the lid and blend on high speed until smooth and creamy, about 30-60 seconds. Stop and scrape down sides as needed. The mixture should be thick, vibrant, and well combined.
Adjust texture: If too thick, add a splash more coconut milk and blend briefly. If too thin, add more ice and blend again until desired consistency is reached.
Pour the smoothie into glasses and sprinkle the toasted coconut shavings generously on top as a garnish. Serve immediately with a straw or spoon.