In a microwave-safe bowl, combine glutinous rice flour and sugar, whisking until evenly blended. Gradually pour in water while stirring to create a smooth batter.

Cover with a wet paper towel and microwave on high for 1 minute, stir, then repeat for another minute and again.

Allow the mochi mixture to cool for 5-10 minutes at room temperature.

Dust a clean surface with cornstarch and transfer the cooled mochi dough onto it.

Using a sharp knife dusted with cornstarch, cut the mochi dough into eight equal squares.

Flatten each mochi square and add small chunks of banana in the center.

Pinch the sides around the banana filling to seal the mochi.

Serve immediately, or refrigerate for an hour for a cool treat.