Chop mangoes into small, bite-size pieces; place in a medium microwave-safe bowl.

Drizzle honey over mangoes and microwave until warm (about 2 minutes).

Mix together oats, hot water, and cinnamon; cook in a large microwave safe bowl for 2 minutes, stirring halfway through and checking frequently to make sure it doesn't boil over.

Stir in the mango with honey.

Sprinkle with walnuts and a splash of milk (if desired).