Peel and chop the mangoes into small chunks. If using frozen mango, let it thaw slightly.
Blend mango chunks, water, sugar, lime juice, chili powder, and salt in a blender. Mix until completely smooth.
Taste the mix. Add more sugar or chili depending on how sweet or spicy you want it.
(Optional) Strain the mixture through a fine mesh strainer for a smoother texture.
Chill the mixture in the fridge for 1 hour.
Pour into an ice cream maker and churn according to the manufacturer’s directions (usually 20–25 minutes), until it reaches soft-serve consistency.
If you don’t have an ice cream maker, pour the mix into a shallow container and freeze. Stir it every 30–45 minutes for about 3 hours to break up ice crystals.
Transfer to a freezer-safe container and freeze until firm—2 to 3 hours.
Scoop and serve. Sprinkle with Tajín or extra chili powder before serving if you want that extra pop.